[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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