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Disk speed on different partitions (was: Re: ext2/ext3/vfat on laptop vs. desktop)

2nd try. With attachments.

On Fri, 19 Mar 2004, Micha Feigin wrote:

> > After I switched to ext3 on my installation partition (Acer TM 803, Debian
> > stable/testing, based on Knoppix 3.2, heavily upgraded, kernel 2.4.24) I
> > noticed a severe performance loss. Actually, the system suddenly felt
> > quite sluggish (especially during start-up). I did some hdparm -t runs and
> > discoverd that the transfer rate had dropped to around 12.9 MB/s from
> > around 20 MB/s. That is a 30 % drop! I cross-checked with my desktop
> > installation (basically the same setup, but of course very different
> > hardware) and I only noticed (if at all) a drop in transfer rate of about
> > 1 or 2 percent between ext3 and ext2. Also, the vfat partition on the
> > laptop delivers the good old 20 MB/s as did the ext2 partition. On the
> > desktop there is also only a small difference between vfat and ext3.
> >
> > Any ideas why this happened? And yes, I have enabled DMA and manually
> > switched to UDMA 5 on all concerned drives.
> > Should I go back to ext2?
> >

Well, actually I went back to ext2 and only to find out: that was not the
reason for the disk to behave slowly. I have tried to locate the real
reason, but with not much success so far. I also tried to follow Micha'a
advice and did some testing:

>
> Try running top in parallel to doing some heavy disk activity but
> something that is supposed to be low on memory (try moving a bunch of
> files around) and check the cpu load (or anything else that can show
> you cpu load).

I used the bonnie++ benchmark program. The results (in html) are attached.
The difference in sequential reads is apparent: 16771 K/sec for the
Windows partition (vfat) as opposed to only 12176 K/sec for the Linux/ext2
partition. That's a 25% difference.

Question1 : could this be related to the position of the partition on the
disk? How could I verify this? Is the hda2 partition always directly
adjacent to the hda1 partition? I have re-partitioned the disk sometime in
the past (before I noticed the performance loss). Maybe the Linux
partition got (unintentionally) moved to the end of the disk?

Question2 : Why does this not happen on my Desktop? I also have a
Windows/vfat partition (at the beginning of the disk) and a Linux/ext3
partition somewhere else on the disk, but there is *no* difference in
disk I/O.

I am at a loss. Any help?
Cheers, Stefan (debian @ goessling . de)
Title: Bonnie++ V1.03 Benchmark results
Sequential Output Sequential Input Random
Seeks		 Sequential Create Random Create
Size:Chunk SizePer CharBlockRewritePer CharBlockNum FilesCreateReadDeleteCreateReadDelete
K/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU
entropy1G1229748120402511801025037121761101.5016439498++++++++++++++++470599++++++++20103100
Title: Bonnie++ V1.03 Benchmark results
Sequential Output Sequential Input Random
Seeks		 Sequential Create Random Create
Size:Chunk SizePer CharBlockRewritePer CharBlockNum FilesCreateReadDeleteCreateReadDelete
K/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU/ sec% CPU
entropy1G82933310220268921144035416771398.0216519713498151710056881679824499
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