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 *HyperDrive5* 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> wrote: > > From: Bob Friesenhahn [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. > > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
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