Performance of a USB ZIL for ZFS

Damien Fleuriot ml at
Mon Jun 27 09:56:52 UTC 2011

On 6/26/11 7:25 AM, Joshua Isom wrote:
> On 6/25/2011 9:32 PM, Damien Fleuriot wrote:
>> On 25 Jun 2011, at 19:17, Joshua Isom<jrisom at>  wrote:
>>> I was wondering if anyone had tried using a decent USB flash drive
>>> for the ZIL.  I know it'd be hard finding one fast enough, but some
>>> from patriot seem like they might be suitable for home use.  Part of
>>> the idea is to just minimize hard drive thrashing and the wear and
>>> tear associated with it.  If it helps prevent the drives from going
>>> bad, and doesn't hurt performance too bad all the better.  But if
>>> it's going to hurt performance too much or not help prevent thrashing
>>> there isn't a point.
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>> I stopped reading at the title.
>> The answer is no.
>> Grab a SSD for $80-120ish.
> Perhaps it would have helped to read the email.  Part of the concern is
> making sure the drives don't fail and not just throughput.
> Given that Kingston sells an SATA SSD for $40 that only gets writes at
> 30mb/s write, and some USB drives might get up to 20mb/s.  If I get two
> drives and put them on different controllers, mirrored, I might get
> acceptable performance.  I may still loose performance, but if my drives
> last a year longer, I can probably accept it.  I'm ok with loosing some
> performance, but I just don't want it dragging down the system.  And if
> it won't help the drives last longer there's no point.

What do you want to do here, data security or performance ?

Having a dedicated ZIL is accepted to be a performance concern, more
than security.

Obviously you'll do as you please, but I'll tell you what:

If you're going to play cheap and grab a USB key for your ZIL, don't be
surprised when you lose your data and/or experience downtime because
your key went boom, or the USB controller hung for a sec and your sync

This is data we're talking about, and considering you want a dedicated
ZIL this is probably important and/or voluminous data.

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