[TriLUG] Linux NFS - ESX VAAI plugin

[Ron Kelley via TriLUG]

Thanks for the detailed info.  I don’t clone many VMs, but I was hoping to take advantage of VAAI if I could.  Based on your notes below, it seems VAAI would be filesystem specific (ie: btrfs, zfs, etc) as NFS is just providing the transport in this case.  If so, your reasoning makes perfect sense.


-Ron


> On Aug 30, 2018, at 2:26 PM, Greg Cox via TriLUG <trilug at trilug.org> wrote:
> 
> On Thu, Aug 30, 2018 at 3:20 PM Ron Kelley via TriLUG <trilug at trilug.org>
> wrote:
> 
>> I have a couple of ESX 5.5 servers mounting an NFS datastore from a CentOS
>> 6 server (nfs v3).
> 
> 
> Obligatory VM-admin cautioning: "5.5's hitting EOS in September.  Upgrade!"
> 
> 
>> After looking over the environment today, I noticed the “NAS VAAI” support
>> is not enabled.  From what I have read, the NAS VAAI offloads some storage
>> commands to the NFS server to make cloning, etc go faster.  To enable this
>> feature, a “vib” package must be installed on each ESX server.
>> 
>> Does anyone know if a generic NFS VAAI plugin exists for “normal” Linux
>> servers (CentOS, Debian, etc)?  Google searching only gives me results for
>> NetApp, Synology, and Hitachi.
> 
> 
> Those vibs that go into each ESXi host are vendor-specific  (you want to
> accelerate a NetApp array, you need a NetApp VIB) and they use the
> proprietary features of the filesystem to speed certain array activities
> up.  For example: "zero out this file" is the same net effect on any
> storage device, and the worst possible way to do it is an over-the-wire
> exchange of "write zeros / I have written zeros / write zeros / I have
> written zeros."
> 
> (wearing NetApp-admin hat) With VAAI disabled/not installed, when you tell
> vCenter "clone this VM", it does all the things you would expect from a
> basic 'cp'.  read a block.  write a block.  lather rinse repeat.  Lots of
> IO from storage array to ESX host, resulting in two thick copies.  With
> VAAI enabled, you saying "clone this VM" becomes an order that goes to the
> storage array, and the array very quickly says "dupe data?  I know how to
> do this myself!" and the storage pounds it out 'by magic': it just happens,
> without the data leaving/reentering the array.
> 
> 
> It doesn't really surprise me that VAAI's not been built for plain Linux,
> because it's not a pragmatic fit.  Linux NFS is pretty small potatoes, and
> VAAI, well, anything that speeds up storage is great, but it is really
> somewhat of a marginal win.  How often are you cloning, anyway?  If you're
> at the point where you're doing so much cloning/zeroing that you could
> benefit from that kind of performance boost, AND you're on Linux for your
> backing datastore, you probably need to switch over to a Real(tm) storage
> array with tons of spindles+space anyway.
> 
> Yes yes, I just slighted Linux on a Linux mailing list.  Oh well.
> -- 
> This message was sent to: Ron Kelley <rkelleyrtp at gmail.com>
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