On 03/05/2015 10:53 AM, Alex Regan wrote:
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.
btrfs is in production now. F21 fully supports it and (I think) it's the
default for F21.
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.
Yes, but again, with a rebuild of a failed drive taking a LONG time, I'm
worried about a second drive going "poof!" during that period. Another
2TB drive seems cheap compared to a degraded RAID5 losing a second drive
during rebuild.
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.
Adaptec is good. MegaRAID also is good and there are monitoring tools
available for OpsView and Nagios to watch it. We use it a lot.
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?
The classic case is SAN attachment via fiberchannel HBAs.
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?
Yup. Our big stuff is in entirely separate racks from the servers.
How about backup applications?
Anything will work. Amanda, Bacula, you name it. We've done it all. It's
more about how reliable your hardware is and what utility you feel
comfortable with.
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?
Look at bacula. It works pretty well.
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