[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

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

On Thu, Feb 09, 2006 at 06:41:11AM +0100, Leo Bogert wrote:
> That is NOT the point and I cannot measure it since all devices are
> RAID5. 

No it isn't the point, but in order to know if it is the filesystem that
is too slow it would potentially be useful to know.

> Now you could have read that from my mail :)
> dd if=/some-large-file of=/dev/zero
> reports 50 MB/s for all large ISO files I have tested it with (more than
> 5, I know what I am doing), and they are not fragmented, I have sorted
> the  fragmented ones out, they even do less speed. 

Well, you did mention AES was involved there too.  You said you tried
aes on a ramdisk too, and got good speed there.  Did you setup aes on a
ramdisk and then put ext3 on it and do file transfers from that?

> dd if=/dev/md1 of=/dev/zero
> reports 100 MB/s, tested with several seek offsets.

Hmm, I didn't know you could write to /dev/zero.  I always use /dev/null
for such things.

> Now it should be very clear to you that the filesystem creates a 50%
> overhead which is inacceptable for a 2800 MHz system. And please read
> my mail again where it is explained that partman probably did not use
> the "stride" option which might be _the_ reason for this overhead. Even
> if you don't accept/understand my problem this still should be fixed as
> the RAID5 HOWTO clearly states.    

Well 50% overhead for the filesystem does sound high.  50% when aes and
the filesystem are involved might be ok.  Are you runing with or without
noatime?  I suspect updating the access times would cause quite a bit of
overhead when aes has to reencrypt all the directory entries to update
the access time stamps.  With noatime mount flag there would be no
writes involved in reading filesystem stuff, while by default with atime
updates enabled it does have to write updates to the filesystem when you
read from it.

> Please forward this mail to the bug-report mailinglist where you wrote to!
> I only receive mails from there and cannot write to it and I don't want my
> bug report to be disregarded because of misunderstandings!  
> My disks are full and I need to fix the problem with the fileserver
> filesystem before it gets so full that I have no space for reformatting ;)  

I assume that is debian-boot@lists.debian.org?

Len Sorensen

Reply to: