I think you would be okay with RAID4, 2 data disk, 1 parity and 1 spare.
Due to the size and speed of SSD, rebuilds are much faster so this is a much more resilient configuration than it would be with a similar configuration and spinning drives. In addition, with the raid group being so small having only 1 spare and 1 parity disk is not such a big deal. I certainly would not recommend no spares as the fact that you can rebuild a failed disk to a hot spare in under a few hours is an important part of the resiliency.
--JMS
From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Basil Sent: Thursday, February 19, 2015 12:14 PM To: Edward Rolison Cc: toasters@teaparty.net Subject: Re: FAS2240-4 'cluster' with 4 SSDs
If you don't protect the SSDs and there's a failure, you'll lose data and corrupt the aggregate, I think. For flash pool, at least.
On Thu, Feb 19, 2015 at 11:38 AM, Edward Rolison <ed.rolison@gmail.commailto:ed.rolison@gmail.com> wrote: I'm not overly keen on the concept - these systems aren't particularly performance critical, so can do without. What I'm not clear on is just how weak a link a two drive/no spare RAID4 flashpool would actually be.
I mean, I don't like running without spares at all, but given I believe the flash pool is used like a cache (e.g. not a unique copy, but a replica) is that as much of a risk?
On 19 February 2015 at 16:32, Vervloesem Wouter <wouter.vervloesem@neoria.bemailto:wouter.vervloesem@neoria.be> wrote: I try not to use raid4 in FlashPools. Using raid4 may increase the amount of usable cache size, but this means your SSD raidgroup becomes the weakest link in the aggregate. I would assign all SSD's to one of the nodes and create one SSD raid_dp raigroup.
Mvg, Wouter Vervloesem
Neoria - Uptime Group Veldkant 35D B-2550 Kontich
Tel: +32 (0)3 451 23 82tel:%2B32%20%280%293%20451%2023%2082 Mailto: wouter.vervloesem@neoria.bemailto:wouter.vervloesem@neoria.be Web: http://www.neoria.be
Op 19-feb.-2015, om 16:48 heeft Ed Morgan <Ed.Morgan@ansgroup.co.ukmailto:Ed.Morgan@ansgroup.co.uk> het volgende geschreven:
I’d do 1 head with a flashpool and one without.
From: Edward Rolison <ed.rolison@gmail.commailto:ed.rolison@gmail.com> Date: Thursday, 19 February 2015 15:39 To: "toasters@teaparty.netmailto:toasters@teaparty.net" <toasters@teaparty.netmailto:toasters@teaparty.net> Subject: FAS2240-4 'cluster' with 4 SSDs
Can I sanity check something?
I've got a cluster in a box - in the form of a 2240-4. Single shelf, but it's got 4 SSDs installed.
Which works as two per head.
Looking at it, I can't actually configure a hybrid aggregate, because I have to match RAID types (RAID-DP on two drives doesn't work). That's on my current code rev of 8.1.3
Upgrading to 8.2 might be a solution, because then I could RAID4 my SSDs.
But I'm wondering - what happens, given a system with no spares, one of the SSDs dies? (Or indeed, whether running with no spares is actually a good idea in the first place - I do have spares for my SAS drives, but not SSDs).
With that in mind - am I onto a bit of a loser here? And I should just be looking to replace my SSDs with some drives to match what I've got already?
Or perhaps have one head with flashpool, 3 drives + spare and one without?
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