One more thing I¹d like to add here: The PERC cache measurably and significantly accelerates small disk writes. However, for read operations, it is insignificant compared to system ram, both in terms of size and speed. There is no significant performance improvement by enabling adaptive readahead in the PERC. I will recommend instead, the PERC should be enabled for Write Back, and have the readahead disabled. Fortunately this is the default configuration on a new perc volume, so unless you changed it, you should be fine.
It may be smart to double check, and ensure your OS does adaptive readahead. In Linux (rhel/centos) you can check that the ³readahead² service is loading. I noticed this is enabled by default in runlevel 5, but disabled by default in runlevel 3. Interesting. I don¹t know how to check solaris or opensolaris, to ensure adaptive readahead is enabled. On 2/18/10 8:08 AM, "Edward Ned Harvey" <sola...@nedharvey.com> wrote: > Ok, I¹ve done all the tests I plan to complete. For highest performance, it > seems: > · The measure I think is the most relevant for typical operation is the > fastest random read /write / mix. (Thanks Bob, for suggesting I do this > test.) > The winner is clearly striped mirrors in ZFS > > · The fastest sustained sequential write is striped mirrors via ZFS, or > maybe raidz > > · The fastest sustained sequential read is striped mirrors via ZFS, or > maybe raidz > > > Here are the results: > · Results summary of Bob's method > http://nedharvey.com/iozone_weezer/bobs%20method/iozone%20results%20summary.pd> f > > · Raw results of Bob's method > http://nedharvey.com/iozone_weezer/bobs%20method/raw_results.zip > > · Results summary of Ned's method > http://nedharvey.com/iozone_weezer/neds%20method/iozone%20results%20summary.pd> f > > · Raw results of Ned's method > http://nedharvey.com/iozone_weezer/neds%20method/raw_results.zip > > > > > > > > From: Edward Ned Harvey [mailto:sola...@nedharvey.com] > Sent: Saturday, February 13, 2010 9:07 AM > To: opensolaris-disc...@opensolaris.org; zfs-discuss@opensolaris.org > Subject: ZFS performance benchmarks in various configurations > > I have a new server, with 7 disks in it. I am performing benchmarks on it > before putting it into production, to substantiate claims I make, like > ³striping mirrors is faster than raidz² and so on. Would anybody like me to > test any particular configuration? Unfortunately I don¹t have any SSD, so I > can¹t do any meaningful test on the ZIL etc. Unless someone in the Boston > area has a 2.5² SAS SSD they wouldn¹t mind lending for a few hours. ;-) > > My hardware configuration: Dell PE 2970 with 8 cores. Normally 32G, but I > pulled it all out to get it down to 4G of ram. (Easier to benchmark disks > when the file operations aren¹t all cached.) ;-) Solaris 10 10/09. PERC 6/i > controller. All disks are configured in PERC for Adaptive ReadAhead, and > Write Back, JBOD. 7 disks present, each SAS 15krpm 160G. OS is occupying 1 > disk, so I have 6 disks to play with. > > I am currently running the following tests: > > Will test, including the time to flush(), various record sizes inside file > sizes up to 16G, sequential write and sequential read. Not doing any mixed > read/write requests. Not doing any random read/write. > iozone -Reab somefile.wks -g 17G -i 1 -i 0 > > Configurations being tested: > · Single disk > > · 2-way mirror > > · 3-way mirror > > · 4-way mirror > > · 5-way mirror > > · 6-way mirror > > · Two mirrors striped (or concatenated) > > · Three mirrors striped (or concatenated) > > · 5-disk raidz > > · 6-disk raidz > > · 6-disk raidz2 > > > Hypothesized results: > · N-way mirrors write at the same speed of a single disk > > · N-way mirrors read n-times faster than a single disk > > · Two mirrors striped read and write 2x faster than a single mirror > > · Three mirrors striped read and write 3x faster than a single mirror > > · Raidz and raidz2: No hypothesis. Some people say they perform > comparable to many disks working together. Some people say it¹s slower than a > single disk. Waiting to see the results. >
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