Date: Fri, 23 Jul 2010 15:20:51 +0200 From: Attila Nagy <bra@fsn.hu> To: ticso@cicely.de Cc: freebsd-fs@freebsd.org, Bernd Walter <ticso@cicely7.cicely.de>, Ivan Voras <ivoras@freebsd.org> Subject: Re: ZFS makes SSDs faster than memory! Message-ID: <4C499733.5000104@fsn.hu> In-Reply-To: <20100723125051.GM53114@cicely7.cicely.de> References: <4C496EB0.7050004@fsn.hu> <i2c14p$g4f$1@dough.gmane.org> <20100723125051.GM53114@cicely7.cicely.de>
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On 07/23/10 14:50, Bernd Walter wrote: > On Fri, Jul 23, 2010 at 02:15:44PM +0200, Ivan Voras wrote: > >> On 07/23/10 12:28, Attila Nagy wrote: >> >>> Hi, >>> >>> I've came across a strange issue. On a file server (ftp/http/rsync) >>> there is a dual SSD based L2ARC configured for a pool of 24 disks: >>> >> >>> fetch -o /dev/null -4 >>> http://ftp.fsn.hu/pub/CDROM-Images/opensolaris/osol-0906-106a-ai-sparc.iso >>> /dev/null 100% of 493 MB 11 MBps >>> >> If I understand your setup and your benchmark correctly, you are saying >> you have achieved 11 megabytes / s performance out of a volume of 24 >> RAIDZ2 drives split into two parts (so it's like RAID 60). Doesn't this >> number seem extremely low to you, considering that (if recent models) >> each of your drives can probably pull at least 70 MB/s? >> > It is also quite strange that a linear read file gets stored in L2ARC, > which usually holds random accessed data. > Maybe it is very fragmented on disks. > L2ARC with MLC drives usually is much slower than modern disks when > it comes to linear reads. > There is no linear reads here from the PoV of the disks. Exactly one stream of linear read is linear read, but two streams are not. :) Maybe I should have written this first, but I'm not the only one reading from the machine. For random reads even the cheapest MLC outperforms a 7k2 SATA disk (only reads), and this is an Intel stuff, which can do 3000 RIOPS easily. > Are there any facts backup your assumption that data is really > read from memory, SSD, disk in the named cases? > E.g. by ARC/L2ARC and IO statistics. > Yes. When downloading from L2ARC: L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name 0 174 174 21505 0.8 0 0 0.0 13.3| ad4 0 169 169 21479 0.9 0 0 0.0 15.0| ad6 when downloading from ARC: L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name 0 26 19 1129 0.6 7 78 0.4 1.3| ad4 0 19 12 1436 1.1 7 78 0.3 1.4| ad6
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