ZFS on Hardware RAID

[andy thomas]

I have to agree with your comment that hardware RAID controllers add 
another layer of opaque complexity but for what it's worth, I have to 
admit ZFS on h/w RAID does work and can work well in practice.

I run a number of very busy webservers (Dell PowerEdge 2950 with LSI 
MegaRAID SAS 1078 controllers) with the first two disks in RAID 1 as the 
FreeBSD system disk and the remaining 4 disks configured as RAID 0 virtual 
disks making up a ZFS RAIDz1 pool with 3 disks plus one hot spare. 
With 6-10 jails running on each server, these have been running for 
years with no problems at all.

Andy

On Sat, 19 Jan 2019, Rich wrote:

> The two caveats I'd offer are:
> - RAID controllers add an opaque complexity layer if you have problems
> - e.g. if you're using single-disk RAID0s to make a RAID controller
> pretend to be an HBA, if the disk starts misbehaving, you have an
> additional layer of behavior (how the RAID controller interprets
> drives misbehaving and shows that to the OS) to figure out whether the
> drive is bad, the connection is loose, the controller is bad, ...
> - abstracting the redundancy away from ZFS means that ZFS can't
> recover if it knows there's a problem but the underlying RAID
> controller doesn't - that is, say you made a RAID-6, and ZFS sees some
> block fail checksum. There's not a way to say "hey that block was
> wrong, try that read again with different disks" to the controller, so
> you're just sad at data loss on your nominally "redundant" array.
>
> - Rich
>
> On Sat, Jan 19, 2019 at 11:44 AM Maciej Jan Broniarz <gausus at gausus.net> wrote:
>>
>> Hi,
>>
>> I want to use ZFS on a hardware-raid array. I have no option of making it JBOD. I know it is best to use ZFS on JBOD, but
>> that possible in that particular case. My question is - how bad of an idea is it. I have read very different opinions on that subject, but none of them seems conclusive.
>>
>> Any comments and especially case studies are most welcome.
>> All best,
>> mjb
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----------------------------
Andy Thomas,
Time Domain Systems

Tel: +44 (0)7866 556626
Fax: +44 (0)20 8372 2582
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