[mythtv-users] 2 TB Hard Drive Recommendations

[John Drescher]

On Mon, Dec 6, 2010 at 2:20 PM, Kevin Ross <kevin at familyross.net> wrote:
> On 12/06/2010 07:28 AM, Fedor Pikus wrote:
>>
>> Do not use RAID5 with disks over 1TB. Use RAID6. The probability of
>> disk error while reading the whole disk is so high that it is very
>> likely that after replacing a failed disk the array will fail to
>> reconstruct. In RAID5 second fault, even transient, destroys the
>> array.
>>
>
> This isn't 100% true.  You aren't likely to lose the entire array, just a
> few files.  I've had it happen to me. When the second drive starts dropping
> out of the array during a rebuild, you copy that drive using ddrescue to a
> new drive, put the new drive in the array replacing the old one, and let it
> rebuild.  Any bad sectors that ddrescue couldn't recover will be replaced
> with 0's.  This could be in the middle of a file, or in filesystem metadata,
> or completely unused space.  Run an fsck (or equivalent) after the rebuild
> to fix filesystem metadata.  If you're using a filesystem that keeps
> checksums of files, like ZFS or BtrFS, then you'll know which files have
> become corrupt.
>
> Obviously this isn't ideal, but being able to recover as much data as
> possible is better than losing the entire array.

This is one of the benifits to mdraid over hardware raid where it is
often way more difficult to recover from a bad situation.

John