EMC FAST: Whether to File and/or Block Tier

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Storage performance needs in today’s data center can change on a moment’s notice. Data that once needed the backing of a freight train today may only need the performance of a vespa tomorrow. Having the ability to react to the ever changing needs of one’s data in an automated fashion allows efficiencies never before seen in EMC’s midrange product line. Generally as data ages its importance lessens both from a business and usage perspective. Utilizing FAST allows EMC customers to place data on the appropriate storage tier based on application requirements and service levels. Choosing between cost (SATA/NL-SAS) and performance (EFD’s/SAS) is a thing of the past. Below are the what, when and why of EMC’s FAST. The intent is to help one make an informed decision based on the needs of their organization.

Block Tiering (What, When and Why)

The What: FAST for VNX/Clariion is an array based feature that utilizes Analyzer to move block based data (slices of LUNs). By capturing performance characteristics, it can intelligently make predictions on where that data will be best utilized. Data is moved at the sub LUN layer in 1G slices, eliminating the need and overhead with moving the full LUN. This could mean that portions of a LUN could exist on multiple disk types (FC, SATA , EFD) Migrations are seamless to the host and occur bidirectionally based on performance needs, ie. FC to SATA, FC to EFD, SATA to FC, SAS to NL-SAS, etc. FAST is utilized at the Storage Pool layer and not available within Traditional RAID Groups. To utilize FAST v2 (which is sub LUN tiering ) you must be at FLARE 30 or above (, and have both Analyzer and FAST enabler installed on the array. Existing LUNs/Data can migrate seamlessly and non-disruptively into storage pools using the VNX/Clariion LUN migration feature. Additionally FAST operates with other Array based features such as Snapview, MirrorView, SAN Copy, RecoverPoint, etc, without issue. All FAST operations and scheduling is configurable through Unisphere.

The When: Automated tiering is a scheduled batch event and does not happen dynamically.

The Why: To better align your application service levels with the best storage type. Ease of management, as a requirement for FAST are storage pools. Storage pools allow for concise management and eased growth opportunities from one location. Individual RG and Meta LUNs management is not needed to obtain high end services levels with the use of SP’s and FAST. The idea going forth is to minimize disk purchasing requirements by moving hot and cold data to and fro disk types that meet specific service levels for that data. If data is accessed frequently then it makes sense that it lives on either EFD (enterprise FLASH drives) or FC/SAS. If data is not accessed frequently then it ideally should live on SATA/NL-SAS. By utilizing FAST in your environment, you are utilizing your Array in the most efficient manner while minimizing cap-ex costs.

File Tiering (What, When and Why)

The What: FAST for VNX File/Celerra utilizes the Cloud Tiering Appliance (or what was FMA, previously known as Rainfinity). The CTA utilizes a policy engine that allows movement of infrequently used files across different storage tiers based on last access times, modify times, size, filename, etc. As data is moved, the user perception is that the files still exist on primary storage. File retrieval (or recall) is initiated simply by clicking on the file, the file is then copied back to its original location. The appliance itself is available as a virtual appliance that can be imported into your existing VMware infrastructure via vCenter, or as a physical appliance (HW plus the software). Unlike FAST for VNX/CLARiiON, FAST for file allows you to tier across arrays (Celerra <-> VNX, Isilon or third party arrays) or cloud service providers (Atmos namely, other SP’s coming). The introduction of CTA to your environment is non-disruptive. All operations for CTA are configurable through the CTA GUI. In summary, CTA can be used as a Tiering engine, an archiving engine or a migration engine based on the requirements of your business. From an archiving perspective, CTA can utilize both Data Domain and Centera targets for long term enforced file level retention. As a migration engine, CTA can be utilized for permanent file moves from one array to another during technology refreshes or platform conversions. Note: CTA has no knowledge of the storage type, it simply moves files from one tier to another based on pre- defined criteria.

The When: Automated tiering is designed to running at scheduled intervals (in batches) and does not happen dynamically or continually I should say.

The Why: Unstructured data, data that exists outside of pre-defined data model such as SQL, is growing at an alarming rate. Think about how many word docs, excel spreadsheets, pictures, text files exist in your current NAS or general file-served environments. Out of that number what percentage hasn’t been touched since its initial creation? In that context, a fair assessment would be 50% of that data. A more accurate assessment would probably be 80% of your data. Archiving and Tiering via CTA simple allows for more efficient use of your high end and low end storage. If 80% of your data is not accessed or accessed infrequently it has no business being on fast spinning disk (FC or SAS). Ultimately this allows you to curb your future spending on pricey high end disk and focus more purchasing capacity for where your data should sit, on low end storage.


As brought to my attention on the twitters (Thanks->@PBradz and @veverything), there is of course another option. Historically, data LUNs as used by the data movers for file specific data (CIFS, NFS) has only been supported on traditional RAID Group LUNs. With the introduction of the VNX, support has been extended to pool LUNs. This implies that you can utilize FAST block tiering for the data that encompasses those LUNs. A couple of things when designing and utilizing in this manner (more info here)…

  • The entire pool should be used by file only
  • Thick LUNs only within the pool
  • Same tiering policy for each pool LUN
  • Utilize compression and dedupe on the file side. Stay clear of block thin provisioning and compression.

There are of course numerous other recommendations that should be noted if you decide to go this route. Personally, its taken me a while to warm up to storage pools. Like any new technology it needs to gain my trust before I go all in on recommending it. Inherent bugs and inefficiencies early on have caused me to be somewhat cautious. Assuming you walk the line on how your pools are configured, this is a very viable means to file tier (so to speak) with the purchase of FAST block only. That being said there is still benefit to using the CTA for long term archiving primarily off array, as currently FAST Block is array bound only. Define the requirements up front so you’re not surprised on the backend as to what the technology can and can not do. If the partner you’re working with is worth their salt you’ll know all applicable options prior to that PO being cut…

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