#1 2017-05-02 12:56:34

lazydave
Member
Registered: 2017-04-26
Posts: 2

SSD for cache

First of all thank you for this great product!

I see you are recommending in your answers to add an ssd cache. Now I am not an expert on esxi maintenance (just a long time user) but how does this work.

My situation:
(2x) Poweredge r820 with 4 spinning disks in raid 10 and 4 ssd disks in raid 10, Of course Esxi only sees datastores because the ssd's are presented as single volume to esxi by the raid controller.

questions:
- I would like to buy an additional ssd for use as ssd cache how would I need to configure the raid controller?
- Any recommended size for an  SSD cache?
- How to setup this SSD cache within esxi?
- Currently I get speeds of 13 MB/s  (Onediff, initial backup) using 4 gigabit ports on each server, what can I expect of speeds after adding a cache ssd?


Regards Dave

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#2 2017-05-02 14:16:04

Daniel
Moderator
Registered: 2017-04-22
Posts: 60

Re: SSD for cache

Well, we haven't delved much into this subject because it's a general ESXi maintenance task, and nobody will answer that better than VMWare themselves. This is a post at their community forum where the very same question is posed:

https://communities.vmware.com/thread/528353

This article at techrepublic.com covers the procedure:

http://www.techrepublic.com/blog/data-c … g-on-esxi/

Just to add something from my part, I would suggest that if you are very focused in getting the best performance from your host, you could make sure that VM swap files are stored in SSD disks as well, this way if your SSD host cache gets filled up, you will still be swapping to fast devices.

Last edited by Daniel (2017-05-03 09:19:48)

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#3 2017-05-02 14:27:14

lazydave
Member
Registered: 2017-04-26
Posts: 2

Re: SSD for cache

thx for the pointers:

Still the question remains how much speed advantage will it bring? is going from 13 to 30 MB/s or from 13 to 15?

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#4 2017-05-02 15:15:17

Daniel
Moderator
Registered: 2017-04-22
Posts: 60

Re: SSD for cache

Well, nobody can answer that question but your very same empiric experience. There are too many variables implied: NICs, switches, HDs, controllers, size of the VMs, amount of RAM, type of RAM, type of DS (NAs or local HD), protocols (NFS, iSCSI, FC), etc, etc...

Reducing everything to comodity HW: i5, 16 gb of RAM, two regular Seagate HDs on a cheap SATA controller acting as local data stores, plus a 120 gb. Samsung SSD, you could expect a 20% to 30% improve in speed when backing up, but you will notice a general performance improve in general too.

Last edited by Daniel (2017-05-03 09:23:29)

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