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.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.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 82
Mailto: wouter.vervloesem@neoria.be
Web: http://www.neoria.be

> Op 19-feb.-2015, om 16:48 heeft Ed Morgan <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.com>
> Date: Thursday, 19 February 2015 15:39
> To: "toasters@teaparty.net" <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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