Category Archives: Storage Tiering

Is Dell Fluid Enough?

Dell made a huge splash 2 weeks ago in London in their inaugural Dell Storage Forum. They dubbed their storage and management lineup as “Fluid Data Architecture” offering the ability for customers to quickly adapt and automate their business when it comes to storage networking and more importantly, data management.

In the London show, they showcased several key innovations and product development. Here’s a list of their jewels:

  • DR4000 – an inline, content optimized backup deduplication appliance (based on the acquired technology of Ocarina Networks)
  • Compellent Storage Center 6.0 – a major software release
  • Compellent key technology integration with VMware
  • Optimized object storage for Microsoft Sharepoint with the DX6000 Object Storage Platform – DX6000 is an OEM from Caringo
  • Broader support for Dell Force10, PowerConnect and their partner’s Brocade

The technology from Ocarina Networks is fantastic technology and I have always admired Ocarina. I have written about Ocarina in the past in my previous blog. But I was a bit perplexed why Dell chose to enter the secondary dedupe market with a backup dedupe appliance in the DR4000. They are already a latecomer into the secondary deduplication game and I thought HP was already late with their StoreOnce.

They could have used Ocarina’s technology to trailblaze the primary deduplication market. In my previous blog, I mentioned that primary deduplication hasn’t really taken off in a big way, and Dell with the technology from Ocarina could set the standard and establish themselves as the leader of the primary deduplication market space. I was disappointed that they didn’t, not just yet.

The Compellent Storage Center 6.0 release was a major release and it was, for better or for worse, coincided with the departure of Phil Soran, the founder and CEO of Compellent. Phil felt that he can let his baby go and Dell is certainly making the best of what they can do with Compellent as their flagship data storage product.

The major release included 64-bit support for greater performance and scalability and also include several key VMware technologies that other vendors already have. The technologies included:

  • VMware vStorage API for Array Integration (VAAI)
  • Storage Replication Adapter plug-in for VMware Site Recovery Manager (SRM)
  • VSphere 5 client plug-in
  • Integration of Enterprise Manager and VSphere

Other storage related releases (I am not going to talk about Force10 or their PowerConnect solutions here) included Dell offering 16Gbps FibreChannel switches from Brocade and also their DX6000 Object Storage Platform optimized for Microsoft Sharepoint.

I think it is fantastic that Dell is adapting and evolving into a business-oriented, enterprise solution provider and their acquisitions in the past 3 years – EqualLogic, Exanet, Ocarina Networks, Force10 and Compellent – proves that Dell aims to take market share in the storage networking and data management market. They have key initiatives with CommVault, Symantec, VMware and Microsoft as well. And Michael Dell is becoming quite a celebrity lately, giving Dell the boost it needs to battle in this market.

But the question is, “Is their Fluid Data Architecture” fluid enough?” If I were a customer, would I bite?

As a customer, I look for completeness in the total solution, and I cannot fault Dell for having most of the pieces in the solution stack. They have networking in their PowerConnect, Force10 and Brocade. They have SAN in both Compellent and EqualLogic but their unified storage story is still a bit lacking. That’s because we have not seen Dell’s NAS storage yet. Exanet was a scale-out NAS and we have seen little rah-rah about this product.

From a data management perspective, their data protection story gels well with the Commvault and Symantec partnership, but I feel that Dell sales and SEs (at least in Malaysia) spends too much time touting the Compellent Automated Storage Tiering. I have spoken to folks who have listened to Dell guys’ pitches and it’s too one-dimensional. It’s always about storage tiering and little else about other Compellent technology.

At this point of time, the story that Dell sells here in Malaysia is still disjointed, but they are getting better. And eventually, the fluidity (pun intended ;-)) of their Fluid Data Architecture will soon improve.

How will Dell fare in 2012? They had taken a beating in the past 2 IDC’s quarter storage market tracker, losing some percentage points in market share but I think Dell will continue to tinker to get it right.

2012 will be their watershed year.

Storage must go on a diet

Nowadays, the capacity of the hard disk drives (HDDs) are really big. 3TB is out and 4TB is in the horizon. What’s next?

For small-medium businesses in Malaysia, depending on their data requirements and applications, 3-10TB is pretty sufficient  and with room to grow as well. Therefore, a 6TB requirement can be easily satisfied with 2 x 3TB HDDs.

If I were the customer, why would I buy a storage array, with the software licenses and other stuff that will not only increase my cost of equipment acquisition and data management, it will also increase the complexity of my IT infrastructure? I could just slot HDDs into my existing server, RAID it with RAID-0 (not a good idea but to save costs, most customers would do that) and I have a 6TB volume! It’s cheaper, easier to manage with Windows or Linux, and my system administrator doesn’t have to fuss about lack of storage experience.

And RAID isn’t really keeping up with the tremendous growth of HDD’s capacity as well. In fact, RAID is at risk. RAID (especially RAID 5/6) just cannot continue provide the LUN or volume reliability and data availability because it just takes too damn long to rebuild the volume after the failure of a disk.

Back in the days where HDDs were less than 500GB, RAID-5 would still hold up but after passing the 1TB mark, RAID-6 became more prevalent. But now, that 1TB has ballooned to 3TB and RAID-6 is on shaky ground. What’s next? RAID-7? ZFS has RAID-Z3, triple parity but come on, how many vendors have that? With triple parity or stronger RAID (is there one?), the price of the storage array is going to get too costly.

Experts have been speaking about parity-declustering,  but that’s something that a few vendors have right now. Panasas, founded by one of forefathers of RAID, Garth Gibson, comes to mind. In fact, Garth Gibson and Mark Holland of Cargenie-Mellon University’s Parallel Data Lab (PDL) presented a paper about parity-declustering more than 10 years ago.

Let’s get back to our storage fatty. Yes, our storage is getting fat, obese, rotund or whatever you want to call it. And storage vendors have been pushing a concept in hope that storage administrators and customers can take advantage of it. It is called Storage Optimization or Storage Efficiency.

Here are a few ways you can consider to put your storage on a diet.

  • Compression
  • Thin Provisioning
  • Deduplication
  • Storage Tiering
  • Tapes and SSDs
To me, compression has not taken the storage world by storm. But then again, there aren’t many vendors that tout compression as a feature for storage optimization. Most of them rather prefer to push the darling of data reduction, data deduplication, as the main feature for save more space. Theoretically, data deduplication makes more sense when the data is inactive, and has high occurrence of duplicated data. That is why secondary storage such  as backup deduplication targets like Data Domain, HP StoreOnce, Quantum DXi can publish 20:1 rates and over time, that rate can get even higher.
NetApp also has been pushing their A-SIS data deduplication on primary storage. Yes, it helps with the storage savings in primary but when the need for higher data transfer rates and time to access “manipulated” data (deduped or compressed), it is likely that compression is a better choice for primary, active data.
So who has compression? NetApp ONTAP 8.0.1 has compression now and IBM with its Storewize V7000 started as a compression device. Read about IBM Storewize in my blog here. Dell has Ocarina Networks, which was recently unleashed. I am a big fan of Ocarina Networks and I wrote about the technology in my previous blog. EMC, during the Celerra days of DART has compression but I don’t hear much about it in their VNX. Compression is there, believe me, embedded all the loads of EMC marketing.
Thin Provisioning is now a must-have and standard feature of all storage vendors. What is Thin Provisioning? The diagram below shows you:
In the past, storage systems aren’t so intelligent. You ask for 10TB, you are given 10TB and that 10TB is “deducted” from the storage capacity. That leads to wastage and storage inefficiencies. Today, Thin Provisioning will give you 10TB but storage capacity is consumed as it is being used. The capacity is not pre-allocated as in the past. Thin provisioning is a great diet pill for bloated storage projects. 
Another up and coming feature is storage tiering. Storage tiering, when associated to storage optimization, should include hierarchical storage management (HSM) and tape-out as well. Storage optimization solutions should not offer only in the storage array itself. Storage tiering within the storage array is available with most vendors – IBM EasyTier, EMC FAST2, Dell Fluid Data Management and many others. But what about data being moved out of the storage array? What about reducing the capacity of the data online or near-line? Why not put them offline if there isn’t a need for it?
I term this as Active Archiving, something I learned while I was at EMC. Here’s a look at EMC’s style of Active Archiving:
Active Archiving promotes the concept of data archiving and is not unique only to EMC. Almost all storage vendors, either natively or with 3rd party vendors, can perform fairly efficient data archiving in one way or another. One of the software that I liked (and not unique!) is Quantum Stornext. Here’s a video of how Quantum Stornext helps reduce the fat of the storage.
With the single-copy sharing feature of Quantum Stornext to multiple disparate OSes, there are lesser duplicate files in storage as well.
Tapes have been getting a bad name in the past few years. It has been repositioned and repurposed as an archive medium rather than a backup medium. But tape is the greenest and most powerful storage diet pill around. And we should not be discount tapes because tapes are fighting back. Pretty soon you will be hearing about Linear Tape File System (LTFS). In a nutshell, Linear Tape File System (LTFS) allows you to use the tape almost as if it were a hard disk. You can drag and drop files from your server to the tape, see the list of saved files using a standard operating system directory (no backup software catalog needed), and use point and click to restore. How cool is that!
And Solid State Drives (SSDs) makes sense as well.
There are times that we need IOPS and using spinning drives, we have to set up many disk spindles to achieve the IOPS that we want.  For example, using the diagram below from the godfather of storage, Greg Schulz,
The set of 16 spinning HDD drives on the left can only deliver 3,520 IOPS. The problem is, we have wasted a lot of disk space, as seen in the diagram below. This design, which most customer would be accustomed to, may look cheaper but in actual fact, is NOT.
If the price of a Fibre Channel HDD is RM2,000, the total of 16 would make up RM32,000.00. That is not inclusive of additional power and cooling and rack space and also the data management costs. Assuming the SSDs costs 5 times more than the Fibre Channel HDD. SSDs are capable of delivering very high IOPS. Here I am putting a modest 5,000 IOPS per SSDs. With just 2 SSDs (as the right design suggests), the total costs is only RM20,000. It has greater performance room to grow, and also savings in data management, power and cooling.
Folks, consider SSDs as part of your storage diet plan.
All these features are available, in whole or in part, and they are part of the storage technology offerings that is out there. With all these being said, are you doing something about it? Get off your lazy bum and start managing your storage and put your storage on a diet!!!

Signs of things to come?

I wanted to sign off early tonight but an article in ComputerWorld caught my tired eyes. It was titled “EMC to put hardware into servers, VMs into storage” and after I read it, I couldn’t help but to juxtapose the articles with what I said earlier in my blogs, here and here.

It is very interesting to note that “EMC runs vSphere directly on the storage controllers and then uses vMotion to migrate VMs from application servers onto the storage array, ..” since the storage boxes have enough compute power to run Virtual Machines on the storage. Traditionally and widely accepted, VMs should be running on servers. Contrary to beliefs, EMC has already demonstrated this running of VMs capability on their VNX, Isilon and Symmetrix.

And soon, with EMC’s Project Lightning (announced at EMC World in May 2011), they will be introducing server side PCIe-based SSDs, ala Fusion-IO. This is different from the NetApp PAM/FlashCache PCIe-based card, which sits on their arrays, not on hosts or servers. And it is also very interesting to note that this EMC server-side PCIe Flash SSD card will become a bridge to EMC’s FAST (Fully Automated Storage Tiering) architecture, enabling it to place hot, warm and cold data strategically on different storage tiers of the applications on VMware’s VMs (now on either the server or the storage),  perhaps using vMotion as a data mover on top of the “specialized” link created by the server-side EMC PCIe card.

This also blurs the line between the servers and storage and creates a virtual architecture between servers and storage, because what used to be distinct data border of the servers is now being melded into the EMC storage array, virtually.

2 red alerts are flagging in my brain right now.

  1. The “bridge” has just linked the server back to the storage, after years of talking about networked storage. The server is ONE again with the storage. Doesn’t that look to you like a server with plenty of storage? It has come a full cycle. But more interesting and what I am eager to see is what more is this “bridge” capable of when it comes to data management. vMotion might be the first of many new “protocol” breeds to enhance data management and mobility with this “bridge”. I am salivating right now of this massive potential.
  2. What else can EMC do with the VMware API? This capability I am writing right now is made possible by EMC tweaking VMware’s API to maximize much, much more. As the VMware vStorage API is continually being enhanced, the potential is again, very massive and could change the entire landscape of cloud computing and subsequently, the entire IT landscape. This is another Pavlov’s dog moment (see figures below as part of my satirical joke on myself)

 

Sorry, the diagram below is not related to what my blog entry is. Just my way of describing myself right now. ;-)

I am extremely impressed with what EMC is doing. A lot of smarts and thinking go into this and this is definitely signs of things to come. The server and the storage are “merging again”. Think of it as Borg assimilation in Star Trek.

Resistance is futile!

Storage Tiering – Responsible and Prudent

Does your IT have bottomless budget? If not, storage tiering is likely to be considered as one of IT’s weapons to combat the ever growing need for storage capacity.

Storage tiering is not new and in the past, features such as HSM (Hierarchical Storage Management) and ILM (Information Lifecycle Management) addresses storage tiering in different capacities, ranging for simple aging files movement and migration, to data objects being moved within the data infrastructure of an organization with some kind of workflow and searching capabilities.

Lately, storage tiering, and especially automated storage tiering, has been gaining prominence, thanks to the 2 high profile acquisitions – HP 3PAR and Dell Compellent. According to Wikibon,

Tiered storage is a system of assigning applications to different 
types of storage media based on application requirements. Factors 
considered in the allocation of storage type include the level of 
protection needed, performance requirements, speed of recovery, 
and many other considerations.Since assigning application data to 
specific media may be complex, some vendors provide software for 
automatically managing the process.

For the sake of simplicity, this blog talks about automated storage tiering within the storage array itself, where different data blocks are moved within several tiers to achieve just-right storage provisioning. Why do we need to achieve this “just-right provisioning”? Rather than discussing this from an IT, technical angle, the just-right storage provisioning should be addressed from a business and operational angle, and more rightly so, costs and benefits.

Business and operations are about managing costs and increasing profits. In the past, many storage administrators employ a single storage tier architecture. Using the same type of disks, for example, 146G 10,000RPM Fibre Channel disks, there was usually 1 or 2 RAID levels for the entire data storage requirement. Usually RAID 1+0 volumes/LUNs are for the applications that require the highest performance and availability but they come with a big cost. So, the rest of the data are kept in RAID-5 volumes/LUNs. The introduction of enterprise SATA hard disk drives basically changed the rules of the ball game, giving storage administrators another option, a cheaper alternative to store their data. Obviously, storage vendors saw the great need to address this requirement, and hence created automated storage tiering as part of their offerings.

There are quite a few storage solutions that offers the storage tiering feature, and most of them are automated as well, meaning that the data blocks are moved between the different tiers of storage within the array itself automatically. 3PAR, long before they were acquired by HP, had their Dynamic Autonomic Tiering. Today, with HP, 3PAR offers 2 key strengths in their Autonomic Tiering offering.

  • Adaptive Optimization
  • Dynamic Optimization

As HP puts it,

Not to be outdone, Compellent (also long before its acquisition by Dell) had the Data Progression feature as part of the Automated Storage Tiering offering. In a nutshell, their solution (which is basically similar from a 10,000 feet view with most of the competitors) is shown below.

The idea is to put the most frequently accessed data blocks to the most expensive, fastest, storage tier and then dynamically move the lesser accessed data block to the least expensive, most economical tier.

I have had the privilege to learn more about Compellent (before Dell) technology about 2.5 years ago, thanks to my friends Chyr and Winston, the bosses at Impact Business Solutions. And what Compellent has was pretty cool stuff and I would like to share what I have picked up about Dell Compellent storage solution. But some of the information could be a little out of date.

The foundation of Dell Compellent automated storage tiering feature, called Data Progression, is their Dynamic Block Architecture (as shown below)

From a high level, all data blocks are bunched together into a logical data structure called a page. A page is by default 2MB but can be configured between 512KB and 4MB. The page is the granular unit required to initiate and implement the Data Progression feature in Compellent’s automated storage tiering solution. Every page comes with attached metadata about the page such as

  • When was this page created
  • When was this page last accessed
  • Which RAID level is it currently in (RAID 1+0, RAID-59, RAID-55 and so on)
  • Which Tier does it currently reside (Tier 1, 2 or 3)
  • Which kind of disk track does it live in (Fast or Standard)

Meanwhile, there are different storage Tiers and notably, Tier 1, 2 or 3 where different disk profiles reside. Typically, the SSDs or the 15K RPM disk drives will be in Tier 1, the 10K RPM disk drives will be in Tier 2 and the slowest 7200 RPM disks will be in Tier 3.  Each of the 3 tiers are further divided into the outer Fast disk cylinders (where the platters spin the fastest) and the Standard disk cylinders (running in the inner tracks and slower).

As data chunks or blocks are accessed, their frequency of access and their data movement statistics are gathered in real-time, giving the Compellent solution a fairly good intelligence of how the pages should be laid out on the most relevant tiers. As the pages become more stale, and less relevant, the pages of data chunks are progressively relegated to the lower tiers, while the more active, and most relevant pages relative to importance of access, is progressively promoted to the higher tiers.

Different policies can also be configured to ensure that some important pages stay where they are regardless of their frequency of access or their relevance.

There is a very nice whitepaper from Dell detailing their Data Progression technology.

Another big automated storage tiering player is HP 3PAR. I admit that I don’t know the inner details of the HP 3PAR Dynamic Tiering solution, though I had some glossy lessons from a 3PAR Systems Engineer called Nathan Boeger (thanks to my friends at PTC Singapore, the 3PAR distributor back then) about the same time I learned about Dell Compellent. I hope HP can offer to introduce more in depth of how the 3PAR technology works, now that I have gotten cosy with some of the HP Malaysia’s folks.

Similarly, the other big boys are offering the automated storage tiering solution as well. IBM has been offering Easy Tier for almost 18 months and EMC has its FAST2 for about the same time.

Funnily, the odd one out in this automated storage tiering game is NetApp. I was in a partner conference call about 1 year ago and there were questions asking NetApp about their views of automated storage tiering. At that time of the concall, NetApp did not believe in automated storage tiering, preferring to market their FlashCache PCIe (previously called the PAM card) solution. Take note that the FlashCache is a Read-Only “extension” to their NVRAM, and used to accelerate read operations of WAFL. And also take note that NetApp, at the time of writing, does not have an “engine” that performs automated storage tiering, regardless of how they spin it.

There are also host-based file tiering solutions as well.Since I am familiar with the NetApp universe, Arkivio and Enigma Data Solutions are 2 of the main partners that NetApp works with. Recently NetApp also resells StorNext from Quantum. But note that these host-based solutions are file-based, making them less granular, less dynamic and less efficient. They are usually marketed as file archiving solutions, and the host-based license are usually charged by per TB. In large enterprises, this might make sense but for the everyday Joes (with tight IT budgets), host-based file archiving solutions are expensive. And it is nowhere close to the efficiencies of automated storage tiering.

Overall, automated storage tiering, when applied, should help the IT operations and the organization’s business reduce costs. There is no longer a one-size-fit-all model and associating the right storage tier to the relevance and importance of the data at a very granular sub-LUN/sub-volume level will help any organization define a more prudent approach in managing their data actively and more importantly their cost of operations.

This is called Responsible IT. :-D

All SSDs storage array? There’s more than meets the eye at Pure Storage

Wow, after an entire week off with the holidays, I am back and excited about the many happenings in the storage world.

One of the more prominent news was the announcement of Pure Storage launching its enterprise storage array build entirely with flash-based solid state drives. In addition to that, there were other start-ups who were also offering SSDs storage arrays. The likes of Nimbus Data, Avere, Violin Memory Systems all made the news as well as the grand daddy of solid state storage arrays, Texas Memory Systems.

The first thing that came to my mind was, “Wow, this is great because this will push down the $/GB of SSDs closer to the range of $/GB for spinning disks”. But then skepticism crept in and I thought, “Do we really need an entire enterprise storage array of SSDs? That’s going to cost the world”.

At the same time, we in the storage industry knows that no piece of data are alike. They can be large, small, random, sequential, accessed frequently or infrequently and so on. It is obviously better to tier the storage, using SSDs for Tier 0, 10K/15K RPM spinning HDDs for Tier 1, SATA for Tier 2 and perhaps tape for the archive tier. I was already tempted to write my pessimism on Pure Storage when something interesting caught my attention.

Besides the usual marketing jive of sub-milliseconds, predictable latency, green messaging, global inline deduplication and compression and built-in data integrity into its Purity Operating Environment (POE), I was very surprised to find the team behind Pure Storage. Here’s their line-up

  • Scott Dietzen, CEO – starting from principal technologist of Transarc (sold to IBM), principal architect of Web Logic (sold to BEA Systems), CTO of BEA (sold to Oracle), CTO of Zimbra (sold to Yahoo! and then to VMware)
  • John “Coz” Colgrove, Founder & CTO – Veritas Fellow, CTO of Symantec Data Management group, principal architect of Veritas Volume Manager (VxVM) and Veritas File System (VxFS) and holder of 70 patents
  • John Hayes, Founder & Chief Architect – formerly of  Yahoo! office of Chief Technologist
  • Bob Wood, VP of Engineering – Formerly NetApp’s VP of File System Engineering,
  • Michael Cornwell, Director of Technology & Strategy – formerly the lead technologist of Sun Microsystems’ Sun Storage F5100 Flash Array and also Quantum’s storage architect for their storage telemetry, VTL and DXi solutions
  • Ko Yamamoto, VP of System Engineering – previously NetApp’s director of platform engineering, Quantum DXi director of hardware engineering, and also key contributor to 4-generations of Tandem NonStop technology

In addition to that, there are 3 key individual investors worth mentioning

  • Diane Green – Founder of VMware and former CEO
  • Dr. Mendel Rosenblum – Founder and former Chief Scientist and creator of VMware
  • Frank Slootman – formerly CEO of Data Domain (acquired by EMC)

All these industry big guns are flocking to Pure Storage for a reason and it looks to me that Pure Storage ain’t your ordinary, run-of-the-mill enterprise storage company. There’s definitely more than meet the eye.

On top of the enterprise storage array platform is Pure Storage’s Purity Operating Environment (POE). POE focuses on 3 key storage services which are

  • High Performance Data Reduction
  • Mission Critical Reliability
  • Predictable Sub-millisecond Performance

After going through the deep-dive videos by Pure Storage’s CTO, John Colgrove, they are very much banking the success of their solution around SSDs. Everything that they have done is based on SSDs.  For example, in order to achieve a larger capacity as well as a much cheaper $/GB, the data reduction techniques in global deduplication, high compression and also fine grained thin provision of 512 bytes are used. By trading off IOPS (which SSDs have plenty since they are several times faster than conventional spinning disks), a larger usable capacity is achieved.

In their RAID 3D, they also incorporated several high reliability techniques and data integrity algorithm that are specifically for SSDs. One note that was mentioned was that traditional RAID and especially the parity-based RAID levels were designed in the beginning to protect against an entire device failure. However, in SSDs, the failure does not necessarily occur in the entire device. Because of the way SSDs are built, the failure hotspots tend to happen at the much more granular bit level of the SSDs. The erase-then-write techniques that are inherent in NAND Flash SSDs causes the bit error rate (BER) of the SSD device to go up as the device ages. Therefore, it is more likely to get a read/write error from within the SSDs memory itself rather than having the entire SSD device failing. Pure Storage RAID 3D is meant to address such occurrences of bit errors.

I spoke a bit of storage tiering earlier in this article because every corporation employs storage tiering to be financially responsible. However, John Colgrove’s argument was why tier the storage when there’s plentiful of IOPS and the $/GB is comparable to spinning disks. That is true is when the $/GB of SSDs can match the $/GB of spinning disks. Factors we must also taken into account is the rack-space savings using the smaller profile disks of SSDs, the power-savings costs of SSDs versus conventional HDD-based enterprise storage arrays. In its entirety, there are strong indications that the $/GB of SSD-based systems to match or perhaps lower the $/GB of HDD-based systems. And since the IOPS requirement levels of present-day applications have not demanded super-high IOPS and multi-core processing is cheap, there’s plenty of head-room for Pure Storage and other similar enterprise storage array companies to grow.

The tides are changing for the storage industry and it is good to see a start-up like Pure Storage boldly coming forth to announce their backing for SSDs. It’s good for the consumer and good for the industry. But more importantly, they are driving innovations to rethink of how we build storage arrays. I am looking forward to more things to come.

Solid State Drives … are they reliable?

There’s been a lot of questions about Solid State Drives (SSD), aka Enterprise Flash Drives (EFD) by some vendors. Are they less reliable than our 10K or 15K RPM hard disk drives (HDDs)? I was asked this question in the middle of the stage when I was presenting the topic of Green Storage 3 weeks ago.

Well, the usual answer from the typical techie is … “It depends”.

We all fear the unknown and given the limited knowledge we have about SSDs (they are fairly new in the enterprise storage market), we tend to be drawn more to the negatives than the positives of what SSDs are and what they can be. I, for one, believe that SSDs have more positives and over time, we will grow to accept that this is all part of what the IT evolution. IT has always evolved into something better, stronger, faster, more reliable and so on. As famously quoted by Jeff Goldblum’s character Dr. Ian Malcolm, in the movie Jurassic Park I, “Life finds a way …”, IT will always find a way to be just that.

SSDs are typically categorized into MLCs (multi-level cells) and SLCs (single-level cells). They have typically predictable life expectancy ranging from tens of thousands of writes to more than a million writes per drive. This, by no means, is a measure of reliability of the SSDs versus the HDDs. However, SSD controllers and drives employ various techniques to enhance the durability of the drives. A common method is to balance the I/O accesses to the disk block to adapt the I/O usage patterns which can prolong the lifespan of the disk blocks (and subsequently the drives itself) and also ensure performance of the drive does not lag since the I/O is more “spread-out” in the drive. This is known as “wear-leveling” algorithm.

Most SSDs proposed by enterprise storage vendors are MLCs to meet the market price per IOP/$/GB demand because SLC are definitely more expensive for higher durability. Also MLCs have higher BER (bit-error-rate) and it is known than MLCs have 1 BER per 10,000 writes while SLCs have 1 BER per 100,000 writes.

But the advantage of SSDs clearly outweigh HDDs. Fast access (much lower latency) is one of the main advantages. Higher IOPS is another one. SSDs can provide from several thousand IOPS to more than 1 million IOPS when compared to enterprise HDDs. A typical 7,200 RPM SATA drive has less than 120 IOPS while a 15,000 RPM Fibre Channel or SAS drive ranges from 130-200 IOPS. That IOPS advantage is definitely a vast differentiator when comparing SSDs and HDDs.

We are also seeing both drive-format and card-format SSDs in the market. The drive-format type are typically in the 2.5″ and 3.5″ profile and they tend to fit into enterprise storage systems as “disk drives”. They are known to provide capacity. On the other hand, there are also card-format type of SSDs, that fit into a PCIe card that is inserted into host systems. These tend to address the performance requirement of systems and applications. The well known PCIe vendors are Fusion-IO which is in the high-end performance market and NetApp which peddles the PAM (Performance Access Module) card in its filers. The PAM card has been renamed as FlashCache. Rumour has it that EMC will be coming out with a similar solution soon.

Another to note is that SSDs can be read-biased or write-biased. Most SSDs in the market tend to be more read-biased, published with high read IOPS, not write IOPS. Therefore, we have to be prudent to know what out there. This means that some solution, such as the NetApp FlashCache, is more suitable for heavy-read I/O rather than writes I/O. The FlashCache addresses a large segment of the enterprise market because most applications are heavy on reads than writes.

SSDs have been positioned as Tier 0 layer in the Automated Storage Tiering segment of Enterprise Storage. Vendors such as Dell Compellent, HP 3PAR and also EMC FAST2 position themselves with enhanced tiering techniques to automated LUN and sub-LUN tiering and customers have been lapping up this feature like little puppies.

However, an up-and-coming segment for SSDs usage is positioning the SSDs as extended read or write cache to the existing memory of the systems. NetApp’s Flashcache is a PCIe solution that is basically an extended read cache. An interesting feature of Oracle Solaris ZFS called Hybrid Storage Pool allows the creation of read and write cache using SSDs. The Sun fellas even come up with cool names – ReadZilla and LogZilla – for this Hybrid Storage Pool features.

Basically, I have poured out what I know about SSDs (so far) and I intend to learn more about it. SNIA (Storage Networking Industry Association) has a Technical Working Group for Solid State Storage. I advise the readers to check it out.

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