[ale] backup/restore mail from USB external drive

[Phil Turmel]

On 02/12/2014 06:37 PM, Jeff Hubbs wrote:
> On 2/12/14, 5:00 PM, Lightner, Jeff wrote:
>> <snip>
>>
>> You really should be using RAID6 or RAID10 rather than RAID5 as it is
>> even more redundant (i.e. can survive 2 disks failures).
>>
> And you shouldn't be using RAID5 or RAID6 at all if your drives are
> 750-1000GB or larger.

Raid5 is a problem for such large devices due to the chances of a 2nd
failure while recovering from a 1st error.  The corresponding odds for a
triple error on raid6 are pretty much nil.

Raid5 and raid6 have performance problems with certain workloads, but
that's independent of drive size.  The linux-raid archives have lots of
discussion of both issues.

> Mail and database servers would be two good places to make use of
> snapshotting filesystems.  Note that some email systems that use message
> stores go insane if the message store is not in the state that the rest
> of the email system presumes it's in, so you have to make sure that your
> backup/recovery scheme doesn't capture messages and message
> metadata/index in different states.

Concur.  Snapshotting is very handy.

Phil