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RE: (Severe?) Performance issues with ext3 created on RAID5 with partman


> -----Original Message-----
> From: Lennart Sorensen [mailto:lsorense@csclub.uwaterloo.ca] 
> On Wed, Feb 08, 2006 at 08:02:30AM +0100, Leo Bogert wrote:
> > So the read speed of the RAID5 without any overhead added 
> is 100 MB/s.
> > Now of course, one would first assume that the encryption is the 
> > bottleneck because it uses much CPU power.
> > But I used /dev/shm to benchmark loop-AES also and it was 
> at 270 MB/s.
> As I just replied to the bug report, I see nothing wrong here.
> If one disk does 50M/s, then 2 disks should combined do 
> 100M/s.  Since a
> 3 disk raid5 is 2 stripes of data and 1 stripe of parity 
> information, that is equivalant to 2 data drives and 1 parity 
> drive.  Since you don't use the parity data as a user (only 
> the raid uses it) you get only the effective speed of the 
> number of data drives.  So 100M/s is exactly what you should get.

Please read again. The problem is that although the RAID5 is capable of 100
MB/s the ext3 filesystem limits it to only 50 MB/s which is obviously a very
bad bottleneck.

> I created the RAID5 and ext3fs using the Debian installer.
> Now my problem is: The read speed from the harddisks does not 
> go over exactly 51 MB/s. 

I should have stressed that reading from the ext3 is limited to 51 MB/s.

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