Am 09.07.2012 19:26, schrieb Jarry:
> Hi,
> 
> I'm building small server for VPS-hosting purpose (not decided
> yet, probably KVM or ESXi). Althought it is "non production",
> reliability is still issue for me. I'm considering using two
> small SSD (ie. Intel 313, 24GB, SLC) in hw-raid1 (Adaptec 3805)
> just for hypervisor, and 2xHDD/raid1 for VPS.
> 
> I started looking for info on internet but results are not
> conclusive. Opinions vary from "no problem, use SSD&raid1"
> to "using SSD in raid is not recommended no matter if it is
> SW or HW".  Mostly missing trim-command is mentioned as reason
> for not using SSD in any raid.
> 
> Does anyone have any experience with SSD in raid (SW or HW)?
> Is it safe to use it on server?
> 
> Jarry

I don't think trim is currently supported in mdaid. AFAIK dmraid
supports it as long as the RAID controller plays along. I'm unsure about
LVM mirrors.

But trim is not your only issue: mdraid and LVM as well as most (all?)
hardware RAIDs will mirror all blocks from one disk to the other when
you assemble the RAID-1. This means that all blocks on your second SSD
will immediately be marked dirty which incurs a significant performance
penalty.

My advice: Use the second disk to do incremental snapshots of the other
on the filesystem level. Or, if you feel lucky, use btrfs's mirroring
capabilities.

Regards,
Florian Philipp