Re: Raid 10 chunksize - Mailing list pgsql-performance
From | Hannes Dorbath |
---|---|
Subject | Re: Raid 10 chunksize |
Date | |
Msg-id | 49D5C69A.2020009@theendofthetunnel.de Whole thread Raw |
In response to | Re: Raid 10 chunksize (Ron Mayer <rm_pg@cheapcomplexdevices.com>) |
List | pgsql-performance |
Ron Mayer wrote: > Greg Smith wrote: >> On Wed, 1 Apr 2009, Scott Carey wrote: >> >>> Write caching on SATA is totally fine. There were some old ATA drives >>> that when paried with some file systems or OS's would not be safe. There are >>> some combinations that have unsafe write barriers. But there is a >>> standard >>> well supported ATA command to sync and only return after the data is on >>> disk. If you are running an OS that is anything recent at all, and any >>> disks that are not really old, you're fine. >> While I would like to believe this, I don't trust any claims in this >> area that don't have matching tests that demonstrate things working as >> expected. And I've never seen this work. >> >> My laptop has a 7200 RPM drive, which means that if fsync is being >> passed through to the disk correctly I can only fsync <120 >> times/second. Here's what I get when I run sysbench on it, starting >> with the default ext3 configuration: > > I believe it's ext3 who's cheating in this scenario. I assume so too. Here the same test using XFS, first with barriers (XFS default) and then without: Linux 2.6.28-gentoo-r2 #1 SMP Intel(R) Core(TM)2 CPU 6400 @ 2.13GHz GenuineIntel GNU/Linux /dev/sdb /data2 xfs rw,noatime,attr2,logbufs=8,logbsize=256k,noquota 0 0 # sysbench --test=fileio --file-fsync-freq=1 --file-num=1 --file-total-size=16384 --file-test-mode=rndwr run sysbench 0.4.10: multi-threaded system evaluation benchmark Running the test with following options: Number of threads: 1 Extra file open flags: 0 1 files, 16Kb each 16Kb total file size Block size 16Kb Number of random requests for random IO: 10000 Read/Write ratio for combined random IO test: 1.50 Periodic FSYNC enabled, calling fsync() each 1 requests. Calling fsync() at the end of test, Enabled. Using synchronous I/O mode Doing random write test Threads started! Done. Operations performed: 0 Read, 10000 Write, 10000 Other = 20000 Total Read 0b Written 156.25Mb Total transferred 156.25Mb (463.9Kb/sec) 28.99 Requests/sec executed Test execution summary: total time: 344.9013s total number of events: 10000 total time taken by event execution: 0.1453 per-request statistics: min: 0.01ms avg: 0.01ms max: 0.07ms approx. 95 percentile: 0.01ms Threads fairness: events (avg/stddev): 10000.0000/0.00 execution time (avg/stddev): 0.1453/0.00 And now without barriers: /dev/sdb /data2 xfs rw,noatime,attr2,nobarrier,logbufs=8,logbsize=256k,noquota 0 0 # sysbench --test=fileio --file-fsync-freq=1 --file-num=1 --file-total-size=16384 --file-test-mode=rndwr run sysbench 0.4.10: multi-threaded system evaluation benchmark Running the test with following options: Number of threads: 1 Extra file open flags: 0 1 files, 16Kb each 16Kb total file size Block size 16Kb Number of random requests for random IO: 10000 Read/Write ratio for combined random IO test: 1.50 Periodic FSYNC enabled, calling fsync() each 1 requests. Calling fsync() at the end of test, Enabled. Using synchronous I/O mode Doing random write test Threads started! Done. Operations performed: 0 Read, 10000 Write, 10000 Other = 20000 Total Read 0b Written 156.25Mb Total transferred 156.25Mb (62.872Mb/sec) 4023.81 Requests/sec executed Test execution summary: total time: 2.4852s total number of events: 10000 total time taken by event execution: 0.1325 per-request statistics: min: 0.01ms avg: 0.01ms max: 0.06ms approx. 95 percentile: 0.01ms Threads fairness: events (avg/stddev): 10000.0000/0.00 execution time (avg/stddev): 0.1325/0.00 -- Best regards, Hannes Dorbath
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