As there is no 'continuous space' option on ext3/ext2 (or probably "-f
fragment_size" may do a trick?) - I think after some filesystem
activity you simply loose continuous space allocation and rather
expected sequential reading may be transformed into random seeking of
'logically' sequentual blocks...
Rgds,
-Dimitri
On 5/30/07, Albert Cervera Areny <[EMAIL PROTECTED]> wrote:
Hardware isn't very good I believe, and it's about 2-3 years old, but the
RAID
is Linux software, and though not very good the difference between reading
and writing should probably be greater... (?)
Would you set 512Kb readahead on both drives and RAID? I tried various
configurations and none seemed to make a big difference. It seemed correct
to
me to set 512kb per drive and 1024kb for md0.
A Dimecres 30 Maig 2007 16:09, Luke Lonergan va escriure:
> This sounds like a bad RAID controller - are you using a built-in hardware
> RAID? If so, you will likely want to use Linux software RAID instead.
>
> Also - you might want to try a 512KB readahead - I've found that is
optimal
> for RAID1 on some RAID controllers.
>
> - Luke
>
> On 5/30/07 2:35 AM, "Albert Cervera Areny" <[EMAIL PROTECTED]> wrote:
> > Hi,
> > after doing the "dd" tests for a server we have at work I obtained:
> > Read: 47.20 Mb/s
> > Write: 39.82 Mb/s
> > Some days ago read performance was around 20Mb/s due to no readahead in
> > md0 so I modified it using hdparm. However, it seems to me that being it
> > a RAID1 read speed could be much better. These are SATA disks with 3Gb
of
> > RAM so I did 'time bash -c "dd if=/dev/zero of=bigfile bs=8k
count=786432
> > && sync"'. File system is ext3 (if read many times in the list that XFS
> > is faster), but I don't want to change the file system right now.
> > Modifing the readahead from the current 1024k to 2048k doesn't make any
> > difference. Are there any other tweaks I can make?
> >
> >
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> >
> > http://archives.postgresql.org
>
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> TIP 6: explain analyze is your friend
--
Albert Cervera Areny
Dept. Informàtica Sedifa, S.L.
Av. Can Bordoll, 149
08202 - Sabadell (Barcelona)
Tel. 93 715 51 11
Fax. 93 715 51 12
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