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



On Tue, May 13, 2003 at 09:57:22AM -0500, Little, Chris wrote:
> stripe the logical volume across the disks.  add a "-i x" where x is the
> number of volumes in your vg.

I guess this would give performance, but the idea
was to have redundancy and performance where the
latter is a bonus ...

so the RAID 5 stuff is not an option, it is mandatory ;)

best,
Herbert

> 
> > -----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
> > 
> > 
> > 
> > _______________________________________________
> > 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/



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