On Thu, May 15, 2003 at 10:51:44AM +0200, Rick van der Linde wrote: > > > Hi All! > To cut it short LVM on 4 Disc RAID 5 reduces RAW throughput about 45% from 33MB/s to 18MB/s :( > >Has anybody any explanations why the LVM layer eats > >up about 45% of the available throughput? > >(in this configuration?) > > <SNIP results> > > I can't yet tell you why, I see same kind of results with > RAID 5 on 4 IDE disks on seperate channels (as master). > In my case I use an ATA133 and onboard ATA33 controller. > In my case the RAID5 set performs about 50 MB/s and the LVM > about 18 MB/s. I suspect my ATA controller as bottelneck hmm, sounds interesting, especially because you do not get ~ 27MB/s (55%) but 18MB/s the same as I got ... > because my disks which can do 40 MB/s om the ATA133 > controller suddenly operate at 18 MB/s on the ATA33. > That made me decide to buy another ATA100/133 controller. > > As I searched internet on this issue I saw some discussion > about ext3 in combo with md-raid and lvm. What filesystem > did you use on your lvm volume on top of RAID5? yeah, I read something similar, that was the reason why I conducted my tests on the raw partitions (without any filesystem on top ;) > What's fun too is when I use ext3 on RAID5 I see a > performance of about 48 MB/s. > When I use reiserfs it reduces too abou 44 MB/s. > ext2 shows almost the same results as ext3. FYI: at least for ext2/ext3 you should make sure that the 'stride' (raid options for mke2fs) matches the block/stripe size of the underlying RAID configuration ... > Till now I same same results for ext2, ext3 and reiserfs > in my case, however I still suspect my ATA33 channel > to be the bottleneck in my case. When I have another > ATA100/133 controller I'll post new results. many thanks, Herbert > > Rick > > > > > > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
