Tagging a RAID 1 drive as SSD?

[lunadesign]

I'm running two SSDs in RAID 1 on an LSI 9260-8i adapter and ESXi 5.1 lists the RAID 1 virtual drive as "Non-SSD".  I know I can instruct ESXi to recognize it as an SSD, but should I?

What are the advantages and disadvantages of tagging the drive as an SSD?

I've heard that tagging it as an SSD will enable the ability to swap to "host cache".  However, I'm not sure if that's worth doing since the VMs will all be located on the same SSD virtual drive so they will already have the benefits of the speed of the two SSD's.

[lunadesign]

Is there anyone out there that can help with this question?  Pretty please? 

[Linjo]

This blog-post is adressing this:

http://www.yellow-bricks.com/2011/08/18/swap-to-host-cache-aka-swap-to-ssd/

// Linjo

[lunadesign]

Thanks for the response....much appreciated!

That's a great article but I don't think it answered my questions.

Specifically, if my VMs are already on SSDs, does "swap to host cache" make sense?  My hunch is that it only makes sense if the VMs are located on traditional hard drives.

And assuming I'm not using "swap to host cache" are there any other impacts of tagging the SSD RAID-1 array as SSDs or leaving it as "Non-SSD"?

[AndrewAbo]

Given the situation you're referring to, no, you would not see any benefit.  Your VMs already live on the same SSD drives.  The host cache setting only helps when the SSD is faster than the storage (and all connection points in between) on which your VMs reside.  The principle is that it will be faster to write to swap that lives on SSD than it would be on SAN storage - even if the SAN was an SSD SAN, due to the hops to the SAN, the SAN controller(s), networking devices, etc.  The SSD is not only faster read/write (than traditional spinning disk), but being local, the bus to the local SSD has more throughput.
Make sense?

[kspare]

you would see much more performance by using those two ssds and enabling cachecade on the controller. Then the ssd caching is transparent to esxi

[DITGUY2012]

Hope this discussion isn't too old, but we have a similar question. We plan on using slow SATA storage from our netapp SAN as the shared storage but with FusionIO iocache cards on each esx host to provide much higher IO performance on the reads (90/10 for us). FusionIO is much faster than SSD so we're not sure if we should put ssd disk in each host for the swap files so that they're not writing to local disk that's slow for the swapping. We'll have plenty of memory but some applications/os still use the swap file regardless.

Will the use of FusionIO and no memory constraints deflect any benefit of ssd on the host? (poweredge r720).

[DITGUY2012]

Anyone?