Dear Hans and linux-kernel,
I am experiencing read performance loss of between 5 to 20 times
due to what I think is data fragmentation in big files.
I am using linux-2.4.4 with the linux-2.4.4-knfsd-6.g.patch on a
dual processor VIA694 motherboard system with a 40GB Maxtor drive
on the builtin IDE controller DMA enabled and 512MB main memory.
The reiserfs partition is 31GB and about 60-70% full. Also, tail-
packing has not been disabled.
My application consists of 8 programs tied together using MPI.
Each program opens a separate output file and periodically writes
about 200k of data every 10-40 minutes. Some programs run on
remote machines and use the kernel nfsd to write their files on
the server; other programs run directly on the server. It is
possible all 8 programs write at the same time.
In this way 8 data files of about 500MB each are created.
For backup these data files are copied to a second server using
rsync. The second server is identical to the main server in both
hardware and software. Running hdparm -t gives about 20 MB/sec
for each machine. However,
time cat *.dat >/dev/null
reads the data locally on the secondary server 5 to 20 times faster
than reading them locally on the main server.
Main server timings are
real 6m26.789s
user 0m0.210s
sys 0m9.630s
and secondary server timings are
real 0m34.358s
user 0m0.250s
sys 0m9.830s
This is 11 times speed difference. I think the original copies of
the files are quite fragmented. However, I would have expected at
most a two fold decrease in actual performace. Is this reasonable?
I have experienced no other difficulties with reiserfs and like it
very much.
All the best, Eric
Eric Olson wrote:
>
> Dear Hans and linux-kernel,
>
> I am experiencing read performance loss of between 5 to 20 times
> due to what I think is data fragmentation in big files.
>
> I am using linux-2.4.4 with the linux-2.4.4-knfsd-6.g.patch on a
> dual processor VIA694 motherboard system with a 40GB Maxtor drive
> on the builtin IDE controller DMA enabled and 512MB main memory.
>
> The reiserfs partition is 31GB and about 60-70% full. Also, tail-
> packing has not been disabled.
>
> My application consists of 8 programs tied together using MPI.
> Each program opens a separate output file and periodically writes
> about 200k of data every 10-40 minutes. Some programs run on
> remote machines and use the kernel nfsd to write their files on
> the server; other programs run directly on the server. It is
> possible all 8 programs write at the same time.
>
> In this way 8 data files of about 500MB each are created.
>
> For backup these data files are copied to a second server using
> rsync. The second server is identical to the main server in both
> hardware and software. Running hdparm -t gives about 20 MB/sec
> for each machine. However,
>
> time cat *.dat >/dev/null
>
> reads the data locally on the secondary server 5 to 20 times faster
> than reading them locally on the main server.
>
> Main server timings are
>
> real 6m26.789s
> user 0m0.210s
> sys 0m9.630s
>
> and secondary server timings are
>
> real 0m34.358s
> user 0m0.250s
> sys 0m9.830s
>
> This is 11 times speed difference. I think the original copies of
> the files are quite fragmented. However, I would have expected at
> most a two fold decrease in actual performace. Is this reasonable?
>
> I have experienced no other difficulties with reiserfs and like it
> very much.
>
> All the best, Eric
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take a look at zam's new bitmap.c (zam please send), and try changing it around
to see the effect on your app. you'll find the new one is much easier to hack
on.