[OpenIndiana-discuss] Very slow write performance on a 3 disk raidz1-0 zpool

[Bryan Iotti]

Everything I posted about revolved around the impression that you had
terrible performance because of the incorrectly reported block size (many
newer drives do this, it does affect performance in some cases but not this
bad).

Sašo is perfectly right, dedup on a system with 1GB RAM is going to grind
it to a halt.

Disable dedup on the pool, or if you want to do things optimally you could
copy the data off the pool, recreate it with only compression and recopy it
over...

Zpool-12 was mentioned because the system-supplied one only creates pools
with an ASHIFT value of 9. This means that on a 512 byte per block disk the
pool starts properly on a block boundary, while on a 4k per block Advanced
Format drive it starts mid-block (hope I got this right, holler if I'm
wrong) and the whole pool is skewed, with the disk controller working in XP
compatibility mode and yielding poor performance. For this reason someone
created zpool-12, a modified version of the zpool command that allows you
to specify the ASHIFT value and avoid this issue. Still won't prevent the
freakin' firmware on the Caviar Greens from spinning them down very often,
though!

Bryan
 On Aug 24, 2012 12:31 PM, "Julius Roberts" <hooliowobbits at gmail.com> wrote:

> On 24 August 2012 18:02, Bryan Iotti <ironsides.medvet at gmail.com> wrote:
> > Are these Advanced Format Drives (4k sectors) already?
>
> I don't know?
>
> > My own WD Caviar Green 2TB sucked bad before I recreated a pool on it
> with
> > the modified zpool-12 command.
>
> This pool was created in 2008(?) using zfs v10 on solaris express
> developer edition, and was recently upgraded to v5000 or whatever it
> is that comes with OIa5.
>
> > You could run:
> > # zdb <pool name> | grep ashift
> >
> > And see what value you get. If you have 9, the pool is structured for 512
> > byte sectors and a 4k drive could suffer a performance loss. For a 4k
> > drive, the ASHIFT value should be 12.
>
> twsadmin at darling:~/mdbackup/today$ sudo zdb Backups | grep ashift
> Password:
>                 ashift: 9
>                 ashift: 9
> ^C
>
> What does this mean exactly and what is the expected performance loss
> in this situation?
>
> --
> Kind regards, Jules
>
> <golgy> whats so wrong with plumb?
> <hoolio> nothing, in itself.  it's just for me, knowing what it means
> infers i cannot any longer pretend to not be a complete square when it
> comes to computers
> <Gryphon> I don't know that knowing anything about plumb turns you
> into a nerd, but this conversation already has
> <hoolio> are you calling me nerdy?
> <checkers> hoolio: you know what initramfs means, AND does. You're
> lost to the non-geek world already
> <Gryphon> yes
> <hoolio> hrm
> <hoolio> goodbye cruel world.
>
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