Assistance building a backup server

[Alex Regan]

Hi,

>> I currently have a 3TB backup system using five 1TB disks in RAID5.
>> Restore times in case of disk failure are already exceedingly long, so
>> I'd like to consider another method of providing redundancy, and would
>> like suggestions.
>
> Five 1TB disks in a RAID5 should give you about 4TB usable storage. Are
> you sure you're not using RAID6 (two parity drives)?

Yes, that's what I also thought. It's been so long since it was built 
that after just checking, I see it's actually only four disks, with two 
other 1TB drives in the system set up as a mirror.

>> I'd like to have 6TB of usable space using 2TB disks.
>
> Four 2TB drives in a RAID5 or five 2TB drives in a RAID6 would give you
> this. I'd vote for the RAID6.
>
>> Is ext4 still best for this?
>
> BTRFS or (gulp!) XFS might be better, although ext4 would work.

Is btrfs used in production? I wasn't sure that it was fully stable yet.

>> Some RAID variant or is there something better?
>
> The bigger the partition (LUN, PV, LV, whatever), the longer the
> recovery times are in case of a disk failure. I run a number of very
> large storage platforms (>500TB) and as soon as any LUN hits the 1TB
> mark, I immediately go to RAID6, simply because there is a possibility
> that a second drive may go bad while the first one is rebuilding. RAID6
> gives me that cushion.

Yes, cool, I'd definitely use RAID6 then. There is that relatively 
larger portion of unusable data, however. It's not so bad on a 500TB 
array, but with just 5TB or 6TB, it's more expensive. It's always about 
tradeoffs, though.

> 1. I prefer using hardware RAID over software RAID. More expensive, but
> I feel it's more reliable.
>
> 2. I like using hot-swappable drive arrays so drive replacement is easy.
>
> 3. I like having my drives from different manufacturing batches because
> (and this is just based on experience--I can't prove it) when one drive
> from a batch dies, another from that same batch with the same number of
> running hours on it will likely die soon.

Good tips. I've got a few Adaptecs in production, but have always been 
worried about 1) having to be physically at the machine to fix the 
serious (any?) problems 2) increased sense of general lack of control 
and more of a feeling of one wrong move destroys the whole array, 3) 
lack of status reporting without being in the GUI.

I believe Adaptec has some remote logging capabilities, but historically 
it's been limited and perhaps even now only on certain models.

>> Are there any NAS projects that may be beneficial?
>
> The underlying technology of the drive arrays will be the same in a
> NAS as a SAN. It's only the access method that's different and the fact
> that some attributes (permissions, ACLs, etc.) may not be translatable
> between the native system and a NAS. Generally they are translatable on
> a SAN (and I include raw SAN LUNs shared via iSCSI in this) simply
> because it is a directly coupled system and uses the host's native
> filesystems.

I thought SANs were generally attached via iSCSI, correct? There are 
cases where they are not? Maybe over dedicated ethernet?

That's a much bigger proposition, but interesting idea. This creates the 
ability for a separate enclosure dedicated to storing the array's disks, 
correct?

How about backup applications?

I'm currently using rsync with the --hard-links option and a shell 
script built years ago. It was built before Amanda had support for 
spanning tapes/disks.

Is there something that's robust and easier to setup than Amanda?

Thanks,
Alex