13 aug 2008 kl. 17.13 skrev Decibel!:
> On Aug 11, 2008, at 9:01 AM, Jeff wrote:
>> On Aug 11, 2008, at 5:17 AM, Henrik wrote:
>>
>>> OK, changed the SAS RAID 10 to RAID 5 and now my random writes are
>>> handing 112 MB/ sek. So it is almsot twice as fast as the RAID10
>>> with the same disks. Any ideas why?
>>>
>>> Is the iozone tests faulty?
>>
>>
>> does IOzone disable the os caches?
>> If not you need to use a size of 2xRAM for true results.
>>
>> regardless - the test only took 10 seconds of wall time - which
>> isn't very long at all. You'd probably want to run it longer anyway.
>
>
> Additionally, you need to be careful of what size writes you're
> using. If you're doing random writes that perfectly align with the
> raid stripe size, you'll see virtually no RAID5 overhead, and you'll
> get the performance of N-1 drives, as opposed to RAID10 giving you N/
> 2.
But it still needs to do 2 reads and 2 writes for every write, correct?
I did some bonnie++ tests just to give some new more reasonable numbers.
This is with RAID10 on 4 SAS 15k drives with write-back cache.
Version 1.03b ------Sequential Output------ --Sequential Input-
--Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec
%CP /sec %CP
safecube04 32136M 73245 95 213092 16 89456 11 64923 81 219341
16 839.9 1
------Sequential Create------ --------Random
Create--------
-Create-- --Read--- -Delete-- -Create-- --Read---
-Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec
%CP /sec %CP
16 6178 99 +++++ +++ +++++ +++ 6452 100 +++++ +++
20633 99
safecube04,32136M,
73245,95,213092,16,89456,11,64923,81,219341,16,839.9,1,16,6178,99,++++
+,+++,+++++,+++,6452,100,+++++,+++,20633,99
>
> --
> Decibel!, aka Jim C. Nasby, Database Architect decibel@decibel.org
> Give your computer some brain candy! www.distributed.net Team #1828
>
>