On 3/17/2013 6:23 PM, Reginald Beardsley wrote:
Tape as an archival medium has significant issues. Reading poorly stored tapes is a
"one try" proposition w/ no assurance of success. The first high volume
commercial application for digital tape was seismic data acquisition for the oil
industry. The oil companies had very detailed cleaning and retensioning schedules w/ a
large staff to perform them on the tape archives. Absent that level of care, reading old
tapes is very difficult and requires great skill. Old tape is NOT fun to work with.
High capacity tape drives and tapes are not cheap either. Blank LTO tape is
almost as expensive as SATA disk. A ZFS based remote replicating server using
triple parity RAIDZ is probably cheaper than tape. For extremely large volumes
and long archival periods, optical tape is probably the best choice. But then
you're probably working for the government.
I would strongly urge comparing the cost of a ZFS backup server w/ daily
snapshots to the cost of conventional tape backup. I think you'll be quite
surprised at the implications.
reading old disks is a just as significant if not more of an issue, by
my estimation. Try to find a machine that you can do low voltage
differential disks with these days. That was only 15 years ago. what
about SMD? The controllers keep changing over time. Also, after a disk
has been in use for a significant period of time (say years), the
lubrication on the platters tends to evaporate a little bit so that when
you leave it off for a long period of time (days/weeks) it will stick to
the heads and the platters. Tape doesn't have that issue.
An LTO5 tape is about $30 each, better in quantity. 1.5TB, more
depending upon compression. That's an enterprise quality tape with much
longer shelf life than a cheap deskstar disk if cared for properly. Even
the cheap 1TB disks are $70. That's almost a 3X advantage. There's still
a place for tape for archival, and yes, you do have to care for it
properly, just like you have to care for everything else. But, cared for
properly, tape should still outlive disk.
But, used it in its proper place. zfs snapshots make a lot of sense for
online backups!
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