[linux-lvm] LVM on Raid 5 Performance?
Little, Chris
Chris.Little at okdhs.org
Wed May 14 09:07:02 UTC 2003
My understanding is that LVM is not RAID. Where RAID does provide
reliability, LVM allows finer grained control of resources. A side benefit
(and very large benefit) is the ability to stripe for a performance
increase. For us, an Oracle import went from 20 hours to 5 hours when using
striped volumes.
> -----Original Message-----
> From: Herbert Poetzl [mailto:herbert at 13thfloor.at]
> Sent: Wednesday, May 14, 2003 3:22 AM
> To: linux-lvm at sistina.com
> Subject: 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 at 13thfloor.at]
> > > Sent: Tuesday, May 13, 2003 8:37 AM
> > > To: linux-lvm at 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 at 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 at 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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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
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