Messages in this thread |  | | From | Torrey Hoffman <> | Subject | RE: [reiserfs-list] ReiserFS on RAID5 Linux-2.4 - speed problem | Date | Thu, 29 Nov 2001 13:36:08 -0800 |
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René Rebe wrote: [...] > I run ReiserFS on a RAID5 (of 3 IDE disks) using the latest > 2.4.(e.g.16) > kernel for weeks. It works well except that is is painfully > slow. [...]
You are not the only one with these problems...
I am convinced there is a serious, negative performance interaction between software RAID 5 and ReiserFS, at least on IDE. Performance is less than 25% of what it should be.
--------------- Concise summary:
dbench of reiserfs on a normal drive partition is slightly * faster * than timing a raw "dd" from that partition.
But, dbench of reiserfs on a reiserfs on software RAID5 is ** only 1/4 as fast ** as a raw "dd" from the RAID5,
And, to make it worse, software RAID 5 is significantly slower than I think it should be. As a result, my nice RAID 5 is far, far slower than an ordinary partition. These are not just dbench numbers - all sorts of testing shows the problem.
--------------- Here are the details:
I have four Maxtor 60 GB IDE disks, each is master on a single cable, using two Promise Ultra TX2/100 cards. The host is a dual P3-800 with 512 MB of RAM. I bought this hardware specifically to act as a fast, cheap, reliable server... I have no complaints except the speed.
The raid disks are hde, hdg, hdi, hdk, as /dev/md0, not partitioned, /dev/md0 is a single 180 GB reiserfs and is mounted on /home. Chunk size is 1024.
Here's some low level numbers:
Single drive from the RAID: time dd if=/dev/hdg of=/dev/null bs=1M count=1024 - elapsed time 0:37 = 27.65 MB/sec
Raw RAID5: time dd if=/dev/md0 of=/dev/null bs=1M count=1024 - elapsed time 0:25 = 40.96 MB/sec
File on Reiserfs on RAID5: time dd if=/home/test_file_1GB of=/dev/null bs=1M count=1024 - elapsed time 0:33 = 31.03 MB/sec
Old home partition on hda9: time dd if=/dev/hda9 of=/dev/null bs=1M count=1024 - elapsed time 0:41 = 24 MB/sec
dbench tests:
dbench 32 on reiserfs on md0 : 10.7027 MB/sec dbench 32 on reiserfs on hda9 : 27.7925 MB/sec
Note that when I first set this hardware up, I tried RAID0 on the same hardware and saw dbench 32 numbers of 76 MB/sec.
So, I think the dbench number for reiserfs on md0 should be ** at least ** five times faster than it is. Are my expectations too high or is there a real problem here?
(tested on 2.4.15-pre5, this problem has been around for all 2.4 kernels I've tried.)
Happy to help test and debug... please send suggestions.
Torrey Hoffman - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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