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Performance of a USB ZIL for ZFS

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Performance of a USB ZIL for ZFS

Joshua Isom-2
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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Re: Performance of a USB ZIL for ZFS

Fleuriot Damien
On 25 Jun 2011, at 19:17, Joshua Isom <[hidden email]> 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._______________________________________________
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Re: Performance of a USB ZIL for ZFS

Joshua Isom-2
On 6/25/2011 9:32 PM, Damien Fleuriot wrote:

> On 25 Jun 2011, at 19:17, Joshua Isom<[hidden email]>  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.
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Re: Performance of a USB ZIL for ZFS

Dan Nelson
In the last episode (Jun 26), Joshua Isom said:

> On 6/25/2011 9:32 PM, Damien Fleuriot wrote:
> > On 25 Jun 2011, at 19:17, Joshua Isom<[hidden email]>  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.
> >
> > 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.

A seaparate ZIL isn't meant to extend the lifetime of the hard drives; it's
meant to accelerate the speed of sync writes.  Those are pretty infrequent
themselves, unless you're an NFS server.  You'll see a couple syncs per
commit on a database server, but compared to the amount of regular reads and
writes on your average system, you'll save under 1% of the writes by adding
a fast ZIL.  And remember, the ZIL is just a write log.  Everything that
gets written to it will get flushed to disk when zfs writes the next
transaction group.

--
        Dan Nelson
        [hidden email]
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Re: Performance of a USB ZIL for ZFS

Robert Simmons
On 25 Jun 2011, at 19:17, Joshua Isom<[hidden email]>  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.

You question is a good one, but I think the reason for your question may be
off.  If you want the ZIL in a separate location it is to cut down on latency
rather than "thrashing".  See:
http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Disabling_the_ZIL_.28Don.27t.29

If your concern really really is "thrashing" please consider the cost of flash
memory vs a hard drive.  Replacing a bad hard drive is cheaper.  After a
cursory glance at newegg, you can see the price per MB for:
HDD $0.09
USB flash $0.64
SSD $1.875
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Re: Performance of a USB ZIL for ZFS

Fleuriot Damien
In reply to this post by Joshua Isom-2


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<[hidden email]>  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.
>>> _______________________________________________
>>> [hidden email] mailing list
>>> http://lists.freebsd.org/mailman/listinfo/freebsd-questions
>>> To unsubscribe, send any mail to
>>> "[hidden email]"
>>
>>
>> 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
failed.

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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