NetApp FAS Series Review

NetApp do have a “pure” block storage array but it lacks the advanced data services enabled by WAFL


For many years traditional storage array vendors have claimed that their platforms are superior for block storage than NetApp FAS because they do not have the overhead of a Pointer-based Architecture – let’s explore this in more detail:

What do we mean by “pure” block storage?

Uses a Fixed Block Architecture whereby data is always read from and written to a fixed location (i.e. each block has its own Logical Block Address) – in reality most block storage arrays provide the option to use pages (ranging from 5 MB to 1 GB) where the LBA is fixed within the page, but the page can be moved to facilitate tiering.

The advantages of this architecture are:

  1. No performance overhead – it is very easy for the storage array to calculate the location of a block and there is no metadata to cache
  2. No capacity overhead – as there is no additional metadata to manage
  3. No fragmentation – blocks always remain together which enables good sequential IO performance on HDDs
  4. Lends itself to tiering – to automatically place data on the most appropriate drive

The disadvantages of this architecture are:

  1. Advanced data services – cannot be supported:
    1. Granular De-duplication, Compression and Thin Provisioning – typically 4K-32K
    2. Low-overhead snapshots – using Redirect-on-Write rather than Copy-on-Write
    3. Hypervisor technologies like Virtual Volumes (VVOLs) – as VMDKs need to be stored as objects/files
  2. Write performance overhead – especially when using parity RAID (i.e. R5 or R6)
  3. Replication performance overhead – when based on snapshots (as snapshots have a significant overhead)
  4. Separate block and NAS – NAS requires a separately managed file system to be laid on top of the block storage

How does NetApp FAS compare?

FAS uses a Pointer-based Architecture, utilising 4K blocks which can be located anywhere, called WAFL therefore we have to reverse the above list of advantages and disadvantages. NAS based file systems are delivered along with block storage on top of WAFL – block protocols do not sit on top of the NAS protocols instead they interact directly with WAFL.

The good news is that WAFL has been around since 1993 so it is a very mature and highly optimised technology – retrofitting advanced data services to a “pure” block storage array is not straight forward and requires major re-engineering work.

So which is best?

Well we can debate this endlessly and clearly depending on your use case one may be a better choice than the other – 5 years ago this was a valid debate, but to be honest it is a moot point as today all storage platforms have to support the advanced data services listed above and therefore need a Pointer-based rather than Fixed Block Architecture.

Let’s explore some examples of this:

  • VMware
    • Virtual SAN – version 2 will include the Virsto Pointer-based Architecture to enable RoW snapshots and clones, and moving forward many more of the advanced data services
  • EMC
    • VNX/VNXe – uses an 8K Pointer-based Architecture to provide RoW snapshots, De-duplication, Compression and Thin Provisioning
    • XtremIO – uses an 8K Pointer-based Architecture to provide RoW snapshots, De-duplication, Compression and Thin Provisioning
    • VMAX3 – uses 128K tracks to provide RoW snapshots and Thin Provisioning, and in the future support for VVOLs
  • HDS
    • HNAS – uses a 4K/32K Pointer-based Architecture to provide RoW snapshots, De-duplication and Thin Provisioning
    • VSP G1000 – the new Storage Virtualization Operating System (SVOS) was built with VVOLs in mind

It is also worth pointing out that all of the start-up storage vendors that have come onto the market in the last 5 years do not have “pure” block storage platforms – it would just not make sense if they did.

What is interesting is that NetApp do have a “pure” block storage array – the E-Series which provides excellent price/performance, but it lacks the advanced data services enabled by WAFL – also VVOLs support is not expected for some time.

So for me “pure” block storage is no longer sustainable and dismissing products like NetApp FAS because they are not “pure” block no longer makes sense. Moving forward the issue is not that your storage platform has a ground-up all-flash design, but does it have a ground-up Pointer-based Architecture.

“Pure” block storage is dead – long live WAFL and the like.

Disclosure: My company has a business relationship with this vendor other than being a customer: We are Partners with NetApp.
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2 Comments
HenryReal UserTOP REVIEWERTOP 5

Cool. Looking forward to test the new AFA option. I was wonder what's the pros/cons vs Oure

04 May 16
Solutions Architect with 51-200 employeesReal UserPOPULAR
04 May 16
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