[H-GEN] Debian and booting off a RAID mirror partition
Paul Gear
humbug at libertysys.com.au
Thu Jun 21 19:35:11 EDT 2012
On 22/06/12 05:01, Benjamin Fowler wrote:
> ...
> I've built a Debian server on an old HP MediaSmart box. I had the idea
> of using software RAID to make things a little more failure-tolerant,
> however, the disk throughput is not quite what I had expected
> initially -- I did some ad-hoc testing of creating and moving large
> amounts of data around on disk.
>
> I'm after some general advice on approaches to doing disk performance
> troubleshooting on home hardware:
>
> * How do I get an idea of what is 'normal' performance for a given
> hardware configuration?
>
See below from some rough, totally anecdotal results from my VM server.
> * What are common misconfigurations under Linux, that would cause
> poor performance? (I realize there's potentially a lot, if you
> take into account low level configuration, e.g. enabling DMA, LVM,
> software RAID, the filesystem driver itself, partition alignment
> (my disks have 4kb blocks, but yes, my partitions are aligned on
> cylinder boundaries).
>
DMA should be sorted out for you automatically on any recent distro.
The really big one is the BIOS SATA setting: make sure it's on AHCI
(sometimes called "Enhanced"), not ATA/IDE/Compatible/Auto. It can be
up to 20 x difference, depending on the disks.
> * And last but not least, how do I systematically go about finding
> and fixing these kinds of performance issues?
>
Another thing is the type of disk you use. At work we recently bought
some drives from Hitachi & WD's higher-end SATA range (in the $300-350
range rather), and they're a lot faster than the entry-level SATAs
($100-150 range).
Besides the raw drive stuff i've used below, there's also bonnie++,
which is a dedicated filesystem I/O tester.
Regards,
Paul
----- 8< -----
root at enosh:~# lsscsi
[1:0:0:0] disk ATA WDC WD5000AAKS-0 12.0 /dev/sda
[2:0:0:0] disk ATA ST3500320AS SD1A /dev/sdb
[3:0:0:0] disk ATA WDC WD5000AAKS-0 01.0 /dev/sdc
root at enosh:~# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb3[1] sdc3[3] sda3[4]
456156482 blocks super 1.2 [3/3] [UUU]
md1 : active raid1 sdb2[0] sdc2[2] sda2[1]
31246336 blocks [3/3] [UUU]
md0 : active raid1 sda1[0] sdc1[2] sdb1[1]
979840 blocks [3/3] [UUU]
unused devices: <none>
root at enosh:~# hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 122 MB in 3.02 seconds = 40.45 MB/sec
root at enosh:~# hdparm -t /dev/sdb
/dev/sdb:
Timing buffered disk reads: 184 MB in 3.00 seconds = 61.25 MB/sec
root at enosh:~# hdparm -t /dev/sdc
/dev/sdc:
Timing buffered disk reads: 202 MB in 3.05 seconds = 66.21 MB/sec
root at enosh:~# hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 172 MB in 3.02 seconds = 56.89 MB/sec
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