On Mon, 13 Jun 2011, Mathias Burén wrote:
On 13 June 2011 19:30, Tim Blundell <tim.blundell@xxxxxxxxx> wrote:
On 6/11/2011 5:49 AM, Mathias Burén wrote:
=== START OF INFORMATION SECTION ===
Model Family: Western Digital Caviar Green (Adv. Format) family
Device Model: WDC WD20EARS-00MVWB0
Serial Number: WD-WMAZ20188479
Firmware Version: 50.0AB50
User Capacity: 2,000,398,934,016 bytes
Device is: In smartctl database [for details use: -P show]
ATA Version is: 8
ATA Standard is: Exact ATA specification draft version not indicated
Local Time is: Sat Jun 11 10:48:05 2011 IST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
Not certain if this was mentioned. While WDC WD20EARS drives can be used in
an RAID array, WD recommends using there RAID capable drives in an
enterprise environment.
I tried using same drives in a simple RAID-1 array and had serious
performance issues (sync taking a week) and stalls when writing to disk. Are
you using the stock firmware on these drives?
I'm using stock firmware as far as I know (I've not flashed them
manually), and I experience no performance issues. Of course, my
system is limited (RAID6 with an Intel Atom), so I can't really push
them all out to test it. But still, no issues.
I've just put a pair into my own workstation - which is an Atom (2 core/4
threads) with 2GB of RAM, running stock Debian Squeeze, however I've just
installed my own kernel... (2.6.35.13)
They work just fine! Sync took overnight to complete on all partitions.
I'm a fan of multiple partitions, so my /proc/mdstat looks like:
Personalities : [linear] [raid0] [raid1] [raid10]
md1 : active raid1 sdb1[1] sda1[0]
1048512 blocks [2/2] [UU]
md2 : active raid10 sdb2[1] sda2[0]
8387584 blocks 512K chunks 2 far-copies [2/2] [UU]
md3 : active raid10 sdb3[1] sda3[0]
2096128 blocks 512K chunks 2 far-copies [2/2] [UU]
md5 : active raid10 sda5[0] sdb5[1]
922439680 blocks 512K chunks 2 far-copies [2/2] [UU]
md6 : active raid10 sdb6[1] sda6[0]
1019538432 blocks 512K chunks 2 far-copies [2/2] [UU]
And a quick & dirty speed test looks like:
# hdparm -tT /dev/md{1,2}
/dev/md1:
Timing cached reads: 1080 MB in 2.00 seconds = 539.70 MB/sec
Timing buffered disk reads: 352 MB in 3.01 seconds = 116.76 MB/sec
/dev/md2:
Timing cached reads: 1106 MB in 2.00 seconds = 552.92 MB/sec
Timing buffered disk reads: 534 MB in 3.00 seconds = 177.78 MB/sec
which are numbers I'm quite happy with.
md1 is raid1 as I wasn't sure if LILO likes RAID10 yet. It just contains
root. My 'df -h -t ext4' output looks like:
Filesystem Size Used Avail Use% Mounted on
/dev/md1 1008M 235M 722M 25% /
/dev/md2 7.9G 4.2G 3.4G 55% /usr
/dev/md5 866G 178G 645G 22% /var
/dev/md6 958G 200M 909G 1% /archive
With these drives (WDC EARS) it is absolutely essential that you partition
them correctly - partitions *must* start on a 4K aligned boundary (sector
must be evenly divisible by 8) They have a 4K physical sector size, but a
512K logical sector size - and as Linux also uses a 4K block size, then
any mis-alignment seriously degrades drive performance.
Gordon
