[mythtv-users] warning for anyone with western digital green drives

Simon Hobson linux at thehobsons.co.uk
Sat Jan 7 17:28:47 UTC 2012


PJR wrote:
>My two WDC WD10EARX-00N0YB0 (possibly faulty) drives have:
>
>9 Power_on_Hours            190
>193 Load_Cycle_Count     1064
>
>9 Power_on_Hours            175
>193 Load_Cycle_Count     1064
>
>I assume, if they weren't faulty this is not good?

Why faulty ?
The whole essence of this thread is that these drives have (by 
default) very aggressive power saving. If idle for just 8 seconds 
they will unload the heads - which I assume means moving them to a 
safe zone on the disk and lifting them. After this, I suspect there's 
another fairly short timer before they also spin down the drive.

On a typical Unix [like] system, there are frequent disk accesses - 
checking this, logging that, etc, etc. So what tends to happen is the 
drive goes idle, unloads the heads, the system accesses it so it 
loads the heads, rinse and repeat often. So the Load_Cycle_Count 
which counts these will increment quite rapidly.

The suggestion is that it better to increase the timeout, so under 
normal use they won't unload the heads very often, if at all.
Say you accessed the drive every 30 seconds. On each access, the 
drive would load the heads, do the access, then 8 seconds later 
unload the heads again. So that's 120 load cycles per hours, or 2880 
load cycles per day !
Increase the timeout to a minute or two, and under the same scenario 
you'd probably have none.


Which reminds me I need to twiddle with some drives I use for 
backups. I bought a SATA card for the old Mac I use to run 
Retrospect, but kept getting some rather oddball errors, kernel 
panics, and so on. I thought the card might be faulty, but then 
twigged ...
I've done a cron job which every minute updates a file on any of the 
backup disks that are mounted - which prevents the drive going to 
sleep and spinning down. I suspect the load cycle count will be going 
up quite nicely on them - up to 1440 per day while the drive isn't 
actually being accessed by the backup software.
What was happening was that the backup software accesses the drive to 
see what it is, then goes off to find a client - it then scans the 
client, does a bit of thinking to decide what files need copying, and 
then starts copying files by which time the drive has got bored and 
spun down resulting in an error and/or kernel panic.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.


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