Hi!
>>>>> "Jeremy" == Jeremy Hansen <[EMAIL PROTECTED]> writes:
Jeremy> We're doing some mysql benchmarking. For some reason it seems that ide
Jeremy> drives are currently beating a scsi raid array and it seems to be related
Jeremy> to fsync's. Bonnie stats show the scsi array to blow away ide as
Jeremy> expected, but mysql tests still have the idea beating on plain insert
Jeremy> speeds. Can anyone explain how this is possible, or perhaps explain how
Jeremy> our testing may be flawed?
Jeremy> Here's the bonnie stats:
Jeremy> IDE Drive:
Jeremy> Version 1.00g ------Sequential Output------ --Sequential Input- --Random-
Jeremy> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Jeremy> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
Jeremy> jeremy 300M 9026 94 17524 12 8173 9 7269 83 23678 7 102.9 0
Jeremy> ------Sequential Create------ --------Random Create--------
Jeremy> -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
Jeremy> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
Jeremy> 16 469 98 1476 98 16855 89 459 98 7132 99 688 25
Jeremy> SCSI Array:
Jeremy> Version 1.00g ------Sequential Output------ --Sequential Input- --Random-
Jeremy> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Jeremy> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
Jeremy> orville 300M 8433 100 134143 99 127982 99 8016 100 374457 99
1583.4 6
Jeremy> ------Sequential Create------ --------Random Create--------
Jeremy> -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
Jeremy> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
Jeremy> 16 503 13 +++++ +++ 538 13 490 13 +++++ +++ 428 11
Jeremy> So...obviously from bonnie stats, the scsi array blows away the ide...but
Jeremy> using the attached c program, here's what we get for fsync stats using the
Jeremy> little c program I've attached:
Jeremy> IDE Drive:
Jeremy> jeremy:~# time ./xlog file.out fsync
Jeremy> real 0m1.850s
Jeremy> user 0m0.000s
Jeremy> sys 0m0.220s
Jeremy> SCSI Array:
Jeremy> [root@orville mysql_data]# time /root/xlog file.out fsync
Jeremy> real 0m23.586s
Jeremy> user 0m0.010s
Jeremy> sys 0m0.110s
<cut>
Couldn't the problem simply be that the SCSI array is caching things
in RAM before writing to disk while the IDE disk isn't but is flushing
things down to disk at once.
The behaveour of the above would be that when you do a lot of
read/write the SCSI would be much faster, as there is less read/writes
involved, but flush would be slower as there is always unflushed data
in the RAM.
Regards,
Monty
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