dovecot - Jun 2012 - RAID1+md concat+XFS as mailstorage

Hello!

somewhere in maillist I've seen RAID1+md concat+XFS being promoted as
mailstorage.
Does anybody in here actually use this setup?

I've decided to give it a try, 
but ended up with not being able to recover any data off survived pairs from
linear array when _the_first of raid1 pairs got down.

thanks!

On 28/06/2012 13:01, ???????? ????????? ??????????
wrote:
> Hello!
>
> somewhere in maillist I've seen RAID1+md concat+XFS being promoted as
mailstorage.
> Does anybody in here actually use this setup?
>
> I've decided to give it a try,
> but ended up with not being able to recover any data off survived pairs
from linear array when _the_first of raid1 pairs got down.
>
This is the configuration endorsed by Stan Hoeppner.  His description of 
the benefits is quite compelling, but real world feedback is interesting 
to achieve.

Note that you wouldn't get anything back from a similar fail of a RAID10 
array either (unless we are talking temporary removal and re-insertion?)

Ed W

Kelsey Cummings wrote:
> On 06/28/12 05:56, Ed W wrote:
>> So given the statistics show us that 2 disk failures are much more
>> common than we expect, and that "silent corruption" is likely
occurring
>> within (larger) real world file stores,  there really aren't many
battle
>> tested options that can protect against this - really only RAID6 right
>> now and that has significant limitations...
> 
> Has anyone tried or benchmarked ZFS, perhaps ZFS+NFS as backing store 
> for spools?  Sorry if I've missed it and this has already come up. 
> We're using Netapp/NFS, and are likely to continue to do so but still 
> curious.
Hi Kelsey,

We're running ZFS here, and have just started using dovecot on it. No stats
yet to report, but you might be interested in this edge case. One of our server
started behaving badly... the database would randomly crash and not restart due
to corrupted indexed. It turns out that the memory had gone bad, and that it had
been bad for a while. Disk blocks were getting corrupted on read, and some on
write! Luckly because we were on ZFS, which checksums all data, we were able to
detect and repair most of the data (some 80mb of bad blocks distributed evenly
thoughout the entire file system!) automatically, and also know exactly which
files were unrecoverable (in the end just two or three files!). Also, we have
hourly snapshots of all the file systems, so we were able to recover older
versions of those files with minimal loss.

I will never rely on a non-checksumming file system for production use again,
for data that is existed to persist over time.

Joe