stripe the logical volume across the disks. add a "-i x" where x is the number of volumes in your vg. > -----Original Message----- > From: Herbert Poetzl [mailto:herbert@13thfloor.at] > Sent: Tuesday, May 13, 2003 8:37 AM > To: linux-lvm@sistina.com > Subject: LVM on Raid 5 Performance? > > > > Hi All! > > I'm using LVM for a long time, usually on non RAID > systems to simplify storage space modifications ... > > recently I configured a nice system (Dual Athlon, > with 4 18.2G U160 SCSI IBM (DDYS-T18350N) disks > on an Adaptec 29160N Ultra160. Because I had some > troubles with the Adaptec/SCSI cabeling I reduced > the bus speed to 40Mhz, which gives 80MB/s transfer > (theoretically) via SCSI, each disc seems to do > about 15MB/s (which seems a little low). I decided > to arrange the 4 discs in a RAID 5 array to gain > some speedup and redundancy (which resulted in > about 33MB/s burst, 25% below the, again theoretical > limit of 45MB/s). Ontop of the RAID 5 array I > configured LVM 1.0.7 to create several partitions > for further use ... > > Now what happened was, that the performance (read) > dropped to about 18MB/s burst, which wasn't what > I expected at all ... > > Has anybody any explanations why the LVM layer eats > up about 45% of the available throughput? > (in this configuration?) > > raw disc md(raid5) lvm on md > ----------------------------------------------------- > hdparm 14694.40 34129.92 18667.52 > dd 1024k 14988.22 34732.56 18647.98 > dd 32k 15516.06 33945.48 18862.67 > > best, > Herbert > > --- Technical Information --- > > 2.4.21-rc2 kernel (with 1.0.7 LVM patch, among others) > > May 11 05:26:52 phoenix kernel: SCSI subsystem driver Revision: 1.00 > May 11 05:26:52 phoenix kernel: scsi0 : Adaptec AIC7XXX > EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.33 > May 11 05:26:52 phoenix kernel: <Adaptec 29160N > Ultra160 SCSI adapter> > May 11 05:26:52 phoenix kernel: aic7892: Ultra160 > Wide Channel A, SCSI Id=7, 32/253 SCBs > May 11 05:26:52 phoenix kernel: > May 11 05:26:52 phoenix kernel: blk: queue c3667e18, I/O > limit 4095Mb (mask 0xffffffff) > May 11 05:26:52 phoenix kernel: (scsi0:A:0): 80.000MB/s > transfers (40.000MHz, offset 63, 16bit) > May 11 05:26:52 phoenix kernel: (scsi0:A:1): 80.000MB/s > transfers (40.000MHz, offset 63, 16bit) > May 11 05:26:52 phoenix kernel: (scsi0:A:2): 80.000MB/s > transfers (40.000MHz, offset 63, 16bit) > May 11 05:26:52 phoenix kernel: (scsi0:A:3): 80.000MB/s > transfers (40.000MHz, offset 63, 16bit) > > raiddev /dev/md/0 > > raid-level 5 > nr-raid-disks 4 > nr-spare-disks 0 > chunk-size 32 > parity-algorithm left-symmetric > persistent-superblock 1 > > device /dev/hd0/part5 > raid-disk 0 > device /dev/hd1/part5 > raid-disk 1 > device /dev/hd2/part5 > raid-disk 2 > device /dev/hd3/part5 > raid-disk 3 > > > pvcreate /dev/md/0 > vgcreate -A y vgs /dev/md/0 > lvcreate -C y -L 3G -n usr -Z y vgs > > --- Tests --- > > # hdparm -tT /dev/hd0/disc > > /dev/hd0/disc: > Timing buffer-cache reads: 128 MB in 0.50 seconds =256.00 MB/sec > Timing buffered disk reads: 64 MB in 4.46 seconds = 14.35 MB/sec > > # time dd if=/dev/hd0/disc of=/dev/null bs=1024k count=1024 > 1024+0 records in > 1024+0 records out > 0.00user 16.98system 1:09.96elapsed 24%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (111major+274minor)pagefaults 0swaps > > # time dd if=/dev/hd0/disc of=/dev/null bs=32k count=32768 > 32768+0 records in > 32768+0 records out > 0.02user 14.66system 1:07.58elapsed 21%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (110major+26minor)pagefaults 0swaps > > ------------ > > # hdparm -tT /dev/md/0 > > /dev/md/0: > Timing buffer-cache reads: 128 MB in 0.49 seconds =261.22 MB/sec > Timing buffered disk reads: 64 MB in 1.92 seconds = 33.33 MB/sec > > # time dd if=/dev/md/0 of=/dev/null bs=1024k count=1024 > 1024+0 records in > 1024+0 records out > 0.00user 12.09system 0:30.19elapsed 40%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (111major+274minor)pagefaults 0swaps > > # time dd if=/dev/md/0 of=/dev/null bs=32k count=32768 > 32768+0 records in > 32768+0 records out > 0.00user 10.52system 0:30.89elapsed 34%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (110major+26minor)pagefaults 0swaps > > ------------- > > # hdparm -tT /dev/vgs/usr > > /dev/vgs/usr: > Timing buffer-cache reads: 128 MB in 0.50 seconds =256.00 MB/sec > Timing buffered disk reads: 64 MB in 3.51 seconds = 18.23 MB/sec > > # time dd if=/dev/vgs/usr of=/dev/null bs=1024k count=1024 > 1024+0 records in > 1024+0 records out > 0.01user 18.66system 0:56.23elapsed 33%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (111major+274minor)pagefaults 0swaps > > # time dd if=/dev/vgs/usr of=/dev/null bs=32k count=32768 > 32768+0 records in > 32768+0 records out > 0.07user 13.43system 0:55.59elapsed 24%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (110major+26minor)pagefaults 0swaps > > > > _______________________________________________ > 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/
