[mythtvnz] New Hard Drive not performing well

[Steve Holdoway]

On Thu, 2010-11-18 at 11:14 +1300, Ross Williamson wrote:
> Hi all
> 
>  For what it's worth, I had severe performance difficulties on some 1TB 
>  WD Green drives purchased when they first appeared. They did not have 
>  warnings of 4K sector size so it is possible that these were the old 
>  size.
> 
>  I was getting around 1MB/s write speeds which is pretty awful even for 
>  a storage drive, especially with streaming data coming in!
> 
>  After seeing that it was going to take over a week to sync a RAID1 
>  array I thought that there must be some sort of issue here. Many hours 
>  of investigation ensued but what eventually solved it for me was to 
>  disable native command queuing (NCQ) on the particular ports of the SATA 
>  card those drives were on. This can be accomplished in a script on 
>  startup with
> 
>  echo 1 > /sys/block/sda/device/queue_depth
> 
>  (replacing sda with wherever those drives are, obviously)
> 
>  I now get ~8MB/s write speed which, while still on the slow side, is 
>  now adequate for storage.
> 

You've got some of the early EARS drives with the 4k sectors. They
didn't have the warning labels, but *DO* have 4k sectors if the part
number ends with those 4 characters.

It is possible to reformat a mirrored pair in situ with fairly low risk
- half the pair's down while rebuilding the other half. Just a case of
break, reformat, resilver for each half. 

Once done, you're up to decent performance... target is a raid 1 pair of
1TB WD green EARS disks.

sync ; sync ; time ( cp ubuntu-10.04-server-amd64.iso /home/mm ;
sync ;sync )

real	0m15.374s
user	0m0.020s
sys	0m2.300s

So 15 seconds for 710MB is a write speed in excess of 45MB/sec.

Interestingly, not as fast as the reverse ( where the target is a 4 disk
raid 5 partition on old non green 300GB WD disks ) which took 12
seconds.

Steve

-- 
Steve Holdoway <steve at greengecko.co.nz>
http://www.greengecko.co.nz
MSN: steve at greengecko.co.nz
Skype: sholdowa