HyperDrive5 = ACard ANS9010
I have personally been wanting to try one of these for some time as a
ZIL device.
On 12/29/2010 06:35 PM, Kevin Walker wrote:
You do seem to misunderstand ZIL.
ZIL is quite simply write cache and using a short stroked rotating
drive is never going to provide a performance increase that is worth
talking about and more importantly ZIL was designed to be used with a
RAM/Solid State Disk.
We use sata2 *HyperDrive/5/* RAM disks in mirrors and they work well
and are far cheaper than STEC or other enterprise SSD's and have non
of the issue related to trim...
Highly recommended... ;-)
http://www.hyperossystems.co.uk/
Kevin
On 29 December 2010 13:40, Edward Ned Harvey
<opensolarisisdeadlongliveopensola...@nedharvey.com
<mailto:opensolarisisdeadlongliveopensola...@nedharvey.com>> wrote:
> From: Bob Friesenhahn [mailto:bfrie...@simple.dallas.tx.us
<mailto:bfrie...@simple.dallas.tx.us>]
> Sent: Tuesday, December 28, 2010 9:23 PM
>
> > The question of IOPS here is relevant to conversation because
of ZIL
> > dedicated log. If you have advanced short-stroking to get the
write
latency
> > of a log device down to zero, then it can compete against SSD for
purposes
> > of a log device, but nobody seems to believe such technology
currently
> > exists, and it certainly couldn't compete against SSD for
random reads.
> > (ZIL log is the only situation I know of, where write
performance of a
drive
> > matters and read performance does not matter.)
>
> It seems that you may be confused. For the ZIL the drive's
rotational
> latency (based on RPM) is the dominating factor and not the lateral
> head seek time on the media. In this case, the "short-stroking" you
> are talking about does not help any. The ZIL is already effectively
> "short-stroking" since it writes in order.
Nope. I'm not confused at all. I'm making a distinction between
"short
stroking" and "advanced short stroking." Where simple "short
stroking" does
as you said - eliminates the head seek time but still susceptible to
rotational latency. As you said, the ZIL already effectively
accomplishes
that end result, provided a dedicated spindle disk for log device,
but does
not do that if your ZIL is on the pool storage. And what I'm calling
"advanced short stroking" are techniques that effectively
eliminate, or
minimize both seek & latency, to zero or near-zero. What I'm calling
"advanced short stroking" doesn't exist as far as I know, but is
theoretically possible through either special disk hardware or special
drivers.
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