[OpenIndiana-discuss] Raid type selection for large # of ssds

[Grant Albitz]

Thanks for the feedback, they will be either Samsung 830s or if the timing is right 840s. I am sorta leaning toward the zfs equivalent of raid 10 at this point. Do you guys see an issue using all of them in 1 pool/vdev in that scenario?



-----Original Message-----
From: Roy Sigurd Karlsbakk [mailto:roy at karlsbakk.net] 
Sent: Monday, October 8, 2012 12:27 PM
To: Discussion list for OpenIndiana
Subject: Re: [OpenIndiana-discuss] Raid type selection for large # of ssds

> I feel bad asking this question because I generally know what raid 
> type to pick.
> 
> I am about to configure 24 256gig ssd drives in a ZFS/Comstar 
> deployment. This will serve as the datastore for a vmware deployment.
> Does anyone know what raid level would be best. I know the workload 
> will determine alot, but obviously there is varying workload across a 
> vmware environment. Since we are talking about ssds I dont see a 
> particular reason to not create 1 big zfs pool, with the exception 
> that I know people generally try to keep the drive count from getting 
> out of control. Raid 10 seems like a waste of space with little 
> benefit in performance in this case. i am leaning towards raid z2 but 
> wanted to get everyones input.
> 
> The datastore will host a fileserver, and exchange server for about 50 
> users. The environment is all 10g and they have solid states in all 
> desktops so essentially that is the reason for such a large SSD 
> deployment for a small # of users.
> 
> There seems to be varying opinions, especially when you factor in 
> trying to keep writes low for ssds.

I can only share my experience with spinning rust. As others have said, I'd recommend against a single VDEV with all 24 drives. The chance of two or three dying at once is rather high with that number of drives. SSDs die too. A choice of 3x8 in RAIDz2 seems reasonable, or perhaps 2x7+1x8+spare (I know, it's uneven, but not that much, and a spare is a good thing). That'll give you IOPS comparable with 3x IOPS of a single drive, which should be pretty good with most SSDs.

Also, keep in mind the problems with certain (or most?) SATA units connected to a SAS expander. I've seen pretty bad things happen with WD2001FASS drives in such a configuration (we had to replace about 160 drives and replace them with hitachis to solve that problem - not too much data was lost, though, thanks to pure luck).

- What sort of SSDs are these btw?

Vennlige hilsener / Best regards

roy
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Roy Sigurd Karlsbakk
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