On 19/03/17 17:02, Jim Richardson wrote:
> I am not interested in the IBM driver if I can get the ST to work.
I can understand why, but....
There would be significant advantage in using the IBMtape driver over
the generic ST driver if Bacula could be modified to handle its oddity
on forward/back spacing.
The IBMtape driver supports multipathing to tape drives and robots
(Character and Generic devices) which the linux standard ST and SG
drivers don't have. For 99.9% of installations that's irrelevant, but if
you have a multipathed fabric (iscsi, FC or SAS) then it provides a
_major_ leap in robustness and gets rid of the issue of a single drive
or changer showing up as multiple /dev/st* units
The reason for this being a nuisance under ST driver is when you're
using udev and pointing to the drive using /dev/tape/by-id (which is the
only reliable way to get to a drive on a fabric), because on any fabric
disturbance udev may repoint that symbolic link to a different /dev/nst*
- at which point things start breaking badly.
Remember, drives have to be unlocked by the initiator WWID that locked
them and all locks are additive, so what happens is that when the
secondary FC controller issues an unlock and eject command, the drive
doesn't remove the lock that's been set by the primary FC controller,
thern fails to eject and generates an error. The robot will then throw
another error ("removal prevented") which may (or may not) require
manual acknowledgement before it can access other drives and as a reult
the night's backup sequence comes to a an early halt.
(This is also the usual cause of "My tapes won't eject" problems in
robots on SAN fabrics)
The IBMtape driver also has a lot more debugging, logging and monitoring
capablities than the generic ST driver - which is rather long in the
tooth, to say the least.... :)
As far as I've been able to determine, the IBMtape driver doesn't care
if the drives it's talking to are actually IBM or HP ones (they're the
only 2 LTO drive makers left now), so if Bacula could use it, the driver
is a worthwhile addition to any LTO-based backup system.
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Bacula-users mailing list
Bacula-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/bacula-users
