Messages in this thread | | | Date | Tue, 22 Nov 2005 10:48:41 -0500 | From | Bill Davidsen <> | Subject | Re: Performance degradation when using partitions |
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Daniel Nilsson wrote: > While setting up a software RAID-5 array I started looking into the > performance aspect of using partioned drives versus the whole disks > for a RAID-5 array. I have an Adaptec 2400a controller which through > the I2O kernel driver gives me access to 4x 250GB disks (JBOD mode).
Did you get an answer on this? And does it happen if you use the drives directly, /dev/hdN or /dev/sdN instead of using I2O? I didn't see an obvious speed penalty in raw access of drives vs. partitions, but I lacked the hardware to really match your setup, particularly the I2O use vs. direct access to /dev/sd[ef]. > > If I create the raid array on the disks directly, /dev/i2o/hd[abcd] I > can tell from /proc/mdstat that the RAID-5 array is rebuilding at a > rate of about 25MB/sec. If I instead first create one large primary > partition on the drives and then create the raid array on those > partitions /dev/i2o/hd[abcd]1 the array is rebuilding at roughly half > the speed (14MB/sec). > > Not trusting this is a good performance measurement I went ahead and > created a 10GB filesystem (ext3) on top of the resulting 700GB RAID-5 > array just to find that the speed of the resulting array was affected > quite a bit by using partioned drives versus whole disks. Here are the > results, note that the RAID-5 array was still rebuilding while > performing these benchmarks. > > ------Sequential Output------ --Sequential Input- --Random- > --Block-- -Rewrite- ---FS--- --Block-- --Seeks-- > K/sec %CP K/sec %CP K/sec %CP /sec %CP > Whole disks: 44242 16 21290 7 Ext3 56547 12 290.9 0 > > Partitioned: 28383 10 15496 5 Ext3 55089 12 288.9 0 > > > Next step was then to compare performance on just accesses to a single > drive with a filesystem (ReiserFS or ext3) where the file system either > occupied the whole disk or resided in a partition that covered the > whole disk. Here are the results: > > ------Sequential Output------ --Sequential Input- --Random- > --Block-- -Rewrite- ---FS--- --Block-- --Seeks-- > K/sec %CP K/sec %CP K/sec %CP /sec %CP > Whole disk: 61652 20 15886 4 Reiser 25011 3 250.0 0 > 67212 23 16978 4 Ext3 26842 2 234.5 0 > 68275 24 16198 4 Ext3 28969 3 227.0 0 > > Partitioned: 57096 19 16218 4 Reiser 23718 3 252.4 0 > 60934 21 15565 3 Ext3 26900 2 228.7 0 > 60866 21 16219 4 Ext3 26272 2 234.2 0 > > While the results above aren't showing the same kind of drastic > difference as with the raid array it still seems clear that the > partitioned drive is slower on average. I'm on 2.6.14 with a Pentium 4 > 3GHz CPU with SMP and Hyperthreading active. Has anyone else seem > similar results? > > Please CC me and Markus on any replies. > > Thanks > Daniel Nilsson
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