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Re: using a NetBSD host as an iSCSI target for OSX (time machine) (or other mechanisms)
On Nov 16, 2009, at 8:32 AM, Andy Ruhl wrote:
On Mon, Nov 16, 2009 at 4:08 AM, Teemu Rinta-aho <teemu@rinta-
[ ... ]
The short answer to the original question is that you can use USB/FW
disks, Time Capsule or Mac Server. Everything else is not guaranteed
to work, yet.
So long as the remote filesharing system doesn't lie about whether
data actually has been flushed to disk, you should be OK...but that's
"OK" in the sense of "it should work" and not "Apple supports
it". :-) I know of a couple of folks who have combined an Airport or
Time Capsule with the 4-drive Drobo boxes, to obtain multi-terabyte
backup volumes which can actually survive a single disk in the backup
mechanism going down.
However, note that this provides what I'd call online backup and not
long-term archival storage. For the typical home user or small
office, that's probably adequate, but of you're serious about your
data and being able to recover it, get a (S)DLT or LTO tape drive and
execute backup policy where you move some backup tapes offsite
periodically is a far more robust solution.
[ ... ]
When I get time, I will try this. I have a fancy network storage
device (NAS?) that claims to support Time Machine through appletalk (I
think), but it claims to only do it with OSX 10.6, and I don't have
that. I assume they possibly relaxed some requirement for the Time
Machine volume in 10.6 or something?
I'm not an authoritative source (#include <std/disclaimer.h>), but
Time Machine relies heavily on sparse volume support, hard links, and
HFS Journalling, and there were some changes to AFP in 10.5.x to
ensure that sync'ing filesystem data would include syncing the
metadata kept in the journal. So long as you don't lose network
connectivity while taking backups, you should be fine using netatalk
or similar network volumes without this support, but if you do lose
network connectivity, you may be at risk of data loss if you were not
talking to an Apple-supported AFP volume.
TM in 10.6 received a number of improvements-- including a better
understanding of the capabilities and limitations of the backup
volumes being used-- such as supporting overlapping reads to local
disks or concurrent access to hdiutil disk images (if you're not using
a native HFS+/J filesystem on the target volume). Supposedly, HFS+
Journaling implementation was tuned to improve performance when being
used for TM backups, and the amount of network traffic done for remote
backups has been reduced.
Which is how it should be because backing up to a local USB or
firewire disk is not exactly a great idea when it comes to business
critical stuff... But then again, Apple doesn't seem like they care
about business critical stuff as far as I can tell. Time Machine is
really cool until you lose the storage disk, and at that point you're
wishing you used some networked backup solution.
It's probably not useful for me to debate opinions on Apple and
"business critical" stuff, but I would agree with your point that Time
Machine provides online backups which depend on your storage volume(s)
staying alive. Using RAID-1/5/6 storage based upon multiple disks,
which can withstand single-drive failure without losing data, is a
good idea; alternatively, you can also backup a TM storage volume onto
tape or similar to obtain more robust backups.
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