VSphere 5.5 and Virtual Flash Cache / Device - Do You Use It?



  • I have one VCenter instance and 3 ESXi hosts - 1 running 5.5 and 2 running 5.1U1. I was going to upgrade the two that are behind pretty soon. But, while doing some work in VCenter yesterday the virtual flash cache options caught my eye.

    One of the hosts I have runs a SQL 2008 box which serves as the back end database for our Epicor ERP system. There's also a server on that same host that acts as an Epicor application server. The server is a Cisco UCSC-C240-M3S with a couple of Xeon E5-2665 processors, 128 GB RAM, and 16 300 GB 10K SAS drives in OBR 10. Epicor speed is still better than it was before we went virtual (take that, Epicor), but people always want faster. If I could throw a couple of SSDs in some of the 8 extra drive bays we have, it would really give us a boost.

    For those that have used SSDs as a cache device with VSphere 5.5, how much improvement have you seen for database servers? We are about 85/15 read/write but getting closer to 80/20.

    And moreover, how many SSDs should I use for flash in this host if I were to do it?



  • Is that all you have to do, add SSD's and ESXi will do the rest? Do you have to have a certain level of ESXi (like Essentials Plus or Enterprise)?



  • @Dashrender said:

    Is that all you have to do, add SSD's and ESXi will do the rest? Do you have to have a certain level of ESXi (like Essentials Plus or Enterprise)?

    I did not see any version limitations listed here other than needing VCenter:
    http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2058983. So if I read it correctly, the Essentials bundle should work (which is what I have).



  • It is a no-go for us. It seems you must have Enterprise Plus: http://www.vmware.com/products/vsphere/compare. I should have checked there before posting. Maybe someone else will find this helpful.



  • If you have 3 hosts, why not use vSAN? You'll get crazy IOPS, as well as have your data stored across multiple hosts.



  • @Nara said:

    If you have 3 hosts, why not use vSAN? You'll get crazy IOPS, as well as have your data stored across multiple hosts.

    That's definitely the way to go!



  • It's using Cisco UCS that gets you. You give up the amazing performance of Dell or HP with things like CacheCade built in. All that unnecessary FCoE stuff to get out to the disk arrays.



  • Does VMWare just know how to use CacheCade and other Caching tech to make your servers faster? or do you have to tell it how to set it up? Assuming the VM's are 100's of gigs in size, the Cachecade I'm guessing is only a few gigs, how does it decide what goes where?



  • @Dashrender said:

    Does VMWare just know how to use CacheCade and other Caching tech to make your servers faster?

    CacheCade is at the physical storage layer, inside the RAID encapsulation the same as your normal NVRAM cache. VMware has no means of being aware of it. The same as it doesn't know how much RAM the controller has or how many disks are in your array. It just all appears as "an array."



  • @Dashrender said:

    Assuming the VM's are 100's of gigs in size, the Cachecade I'm guessing is only a few gigs, how does it decide what goes where?

    NVRAM is normally 1GB+. CacheCade would rarely be under 200GB and could easily be 500GB.



  • CacheCade is a cache, it decides what stays there in the same way that the RAID cache has always decided that and in the same way that the OS decides what to cache.



  • @scottalanmiller said:

    CacheCade is a cache, it decides what stays there in the same way that the RAID cache has always decided that and in the same way that the OS decides what to cache.

    Awww.. Thanks for that! CacheCade is Dell, what does HP have?



  • @Dashrender said:

    @scottalanmiller said:

    CacheCade is a cache, it decides what stays there in the same way that the RAID cache has always decided that and in the same way that the OS decides what to cache.

    Awww.. Thanks for that! CacheCade is Dell, what does HP have?

    CacheCade is LSI who makes for both.





  • On the Dell side, be aware that you need the RAID controller with the 1GB NV RAM in order to enable cachecade on their servers. Both the H700 and H710P have the capabilities. Dell will tell you that you must use their SSD drives as the cachecade drives, but we have behnchmarked other SSD drives in our lab and verified that they work fine and achieve similar results.



  • @Dashrender said:

    @scottalanmiller said:

    CacheCade is a cache, it decides what stays there in the same way that the RAID cache has always decided that and in the same way that the OS decides what to cache.

    Awww.. Thanks for that! CacheCade is Dell, what does HP have?

    Up to 4GB on-controller Flash-Backed Write Cache (FBWC) - unless I'm doing some extremely large data moves, it feels like I'm writing to flash, even under typical VM workloads.


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