[OpenIndiana-discuss] Mixing zfs raids and mirrors

[Mark]

On 18/10/2011 4:51 a.m., James Carlson wrote:
> Gabriele Bulfon wrote:
>> Hi,
>> I was wondering what (if any) problems I may encounter by mixing different zfs strategies on one pool,
>> with all equal disk sizes.
>> Examples:
>> - pool1: raidz1 a0 a1 a2 mirror a3 a4
>> - pool2: raidz1 b0 b1 b2 raidz1 b3 b4 b5 mirror b6 b7
>> - pool3: mirror c0 c1 mirror c2 c3 raidz c4 c5 c6
>> I'm just trying to balance pools performance and maximum space...
>> Last but not least:
>> - what if pool3 is actually the rpool (where system just occupies few GBytes), where I'll add
>> volumes with quotas to share? Should I keep rpool separate absolutely?
>> (I just don't want to miss many GB on an rpool that will just stay as it is, on the boot disks).
>
> Last I checked, it wasn't possible to boot off of RAID-Z; only mirrors
> were supported for boot.  As for the other part, the man page says:
>
>       Virtual devices cannot be nested, so a mirror or raidz  vir-
>       tual device can only contain files or disks. Mirrors of mir-
>       rors (or other combinations) are not allowed.
>
> If you're looking to boost RAID-Z performance, I'd suggest adding more
> disks.  RAID-Z will effectively stripe the data across the available
> devices, parallelizing the I/O operations.  To get better error
> tolerance, use raidz2 or raidz3.
>
zfs will also complain if your choices are likely to impact performance 
e.g adding a 3 disk raidz to an existing 5 disk raidz.
Performance is optimal when build from the start, since data is evenly 
spread across the available space.

Mark.