Date: Fri, 23 Jul 2010 15:21:42 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-fs@freebsd.org Subject: Re: ZFS makes SSDs faster than memory! Message-ID: <i2c50f$tq9$1@dough.gmane.org> In-Reply-To: <4C4995F7.2080107@fsn.hu> References: <4C496EB0.7050004@fsn.hu> <i2c14p$g4f$1@dough.gmane.org> <4C4995F7.2080107@fsn.hu>
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On 07/23/10 15:15, Attila Nagy wrote: > When pulling this amount of data out of the machine, the disks aren't > saturated, they are at around 10-20% of utilization according to gstat. > BTW, remember that two RAIDZ2 in stripe isn't RAID60. In RAIDZ2 every > read involves a full stripe (er, block) read for checksum validation, > which means at a 128 kiB blocksize and with 12 disks in a RAIDZ2 pool, > all disks provide their part of that 128k read. > That's why a RAIDZ2 pool's IO performance equals of one disk's. Yes, in case of random IOPS you are correct - and in your case it would mean that the files are horribly fragmented (torrent downloads? :)). For sequential IO, even RAIDZ/1/2 will give N-1/2/3 times the performance of a single drive because prefetching will kick in. > The disks in a normal 20-30 MiBps network load do about 30-40 read IOPS, > you are right that they are capable of more (around 100-120). Except for the possible fragmentation issue, I think you should get much better throughput even with 30-40 IOPS per drive.
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