[email protected] wrote: > On Sat, 12 Sep 2009, Doug Hughes wrote: >> yes: http://blogs.sun.com/ahl/entry/fishworks_launch >> But, remember, this is NOT a normal flash drive. > > I had misunderstood you. I thought you were talking about flash > drives, not storage arrays (storage arrays do frequently use DRAM, > they have a full processor on board and large battery packs) > Right, I mixed the logzilla in there as an additional item of interest in technology.
>>>> zfs normally stripes the intent log across the data disks unless >>>> you tell it otherwise (e.g. 46 disks on a Sun x45000 or x4540) >>>> You can also put the ZIL on a dedicated high speed rotating drive. >>>> The x25E outperforms both except in the case where you want high >>>> sequential throughput. >>> >>> well given that the X25E is faster than the rotating storage I would >>> expect it to be a win there as well. >>> >>> but the point I was trying to make was that I suspect most of the >>> benifit is in the step from a striped intent log to an intent log on >>> dedicated media, with the move from there to an X25 helping, but not >>> as much. >>> >> I am trying to correct this misconception. I assure you it's much >> bigger than that for 7200 RPM SATA to X-25E. The latency is lower and >> throughput is higher. But, don't believe me. Check out the references >> I posted earlier. >> Even the consumer X25-M sata SSD is .1msec vs 4.2msec on a 7200RPM >> SATA enterprise drive. for the X25-E it is .085msec for for 15KRPM >> SCSI it is 3.9msec. (The fusion IO is .05 msec) >> >> The raw sequential throughput of the X-25E is close to 3000MB/sec on >> a 64KB record whereas your 9200 RPM drive will be around 100 and the >> 15KRPM drive will be aroudn 227. (it doubles on smaller block sizes) > > I don't doubt your performance number (not much anyway, the X25E is > limited to the speed of sata, so a theoretical limit of 300MB/sec, not > 3000MB/sec ;-), but the huge win (just like it is with databases) is > when you move your intent log off of drives that are seeking all over > the place to a drive where you don't have to seek much, if at all, > letting your writes _be_ sequential in the first place > there was actually not that big of an improvement going from striped across 46 drives to dedicated on 1. There is a huge difference going to ZIL on flash, but again, mainly in NFS acceleration. Local ZFS does decently at buffering up writes in memory and committing them in bulk. _______________________________________________ Discuss mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
