[mythtv-users] 2 TB Hard Drive Recommendations

[John Drescher]

On Tue, Dec 7, 2010 at 5:22 PM, Robin Hill <myth at robinhill.me.uk> wrote:
> On Tue Dec 07, 2010 at 04:02:04PM -0500, John Drescher wrote:
>
>> > Note that Green drives are not recommended for raid arrays because of timing
>> > out and goofing your raid array.  WD's "RE" (RAID Edition) HDDs support
>> > Time-Limited Error Recovery ("TLER" ):
>> >
>> > More info here:
>> >
>> > http://www.tomshardware.com/forum/251076-32-raid-issues-western-digital-hard-disk
>> >
>> > I went WD Black RE's and they are speedy and have been reliable.
>> >
>>
>> TLER is not necessary on linux software raid or zfs raid. It is needed
>> on hardware raid or on windows software raid.
>>
> No idea where you get that from.  Linux software raid is certainly
> affected by read errors causing long lockups (which TLER dramatically
> reduces).  I don't know about ZFS, but I really doubt that it isn't
> affected - working around it would be enormously complicated (you'd need
> to timeout the read request in the driver and fall back to parity, keep
> track of when the drive does actually starts responding again, then deal
> with rewriting the bad block, all the time preventing any other read
> requests to the drive and keeping track of pending writes).
>
> That's not to say that drives without TLER can't be used though - you
> just have to accept the array locking up for 10s of seconds occasionally.
>

The difference is on HW raid or windows software raid or fake raid the
drive will be kicked out of the array during a long delay when the
drive tries to fix a URE. On mdadm the drive will not be kicked out of
the array but it may like you said be offline for > 10 seconds.

John