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RE: [linux-lvm] LVM on Raid 5 Performance?



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: [linux-lvm] 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
> 
> 
> 
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> 



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