[OpenIndiana-discuss] write speeds faster with no ZIL and L2ARC

[Gregory Youngblood]

On Jun 27, 2011, at 2:46 PM, Chris Mosetick wrote:

> Lucas, thank you for your ideas. For over a week I looked at the entirety of
> iostat's output, including asvc_t, %b, %w as you have suggested. Nothing in
> the output seems to be able to explain the transfer speed slowness we
> started experiencing. I'm also completely aware that I can keep adding log
> and cache devices to a single pool. Doing so ignores the truth of the
> matter. Things were humming along just fine with the two X25-E's as log and
> cache, and now things move faster without them configured. I'm pretty sure
> that ZFS is supposed to move at reasonable speeds when on 7200rpm SATA
> disks, and move even faster when low latency log and cache devices are
> configured. At least that's how it has been for me.

Solaris (and OpenSolaris) used to seem like it worked really well with 7200 SATA drives. SAS would be faster, of course, but the SATA were a good option. Of course, lots of concurrent IO could bog it down, and made the SSD for ZIL a requirement. 

I haven't been following the full thread, but is it possible the SSDs are nearing end of life due to limits on write longevity, perhaps it's taking longer for writes to complete now? Is it possible to put a brand new SSD in as a ZIL and see what happens? I don't know, kind of taking a stab in the dark here. 

Hope you get it nailed down. I'll be watching to see what you discover. 

Greg