[comp.os.vms] Current

nagy%43198.hepnet@LBL.ARPA (04/28/87)

>If you ask DEC for their suggested backup technology for VAXclusters
>where you might have multiple RA81's or SA482's they reply TU78's and
>similar which cost a small fortune.
     
All the big (CI) VAXClusters here at Fermilab have TA78 systems which
are used for backups.  My group's LAVCs (Local Area VAXClusters) is
either using RA60s (with pack-to-pack backups) or backing up onto
(ugh) TK50s.

>Can anyone suggest more modern equipments to solve the thorny backup
>problem WHICH ARE RELIABLE AND PROVEN...
     
In my experience, the TA78s are reliable when used primarily for backups.
The main VAXCluster here has 12 TA78s which are HEAVILY used by users
for reading/writing data tapes.  They have intermittent problems with
formatter hangs (discussed in a previous Info-VAX submission).

>How about some of the Megatape products I see (650Mb a cartridge??) or
>WORM optical discs...what are big cluster sites doing now.
     
One thing about TA78s is that they are fast; assuming you have a large
VAX (at least 785, >8500 best) AND that your backup does not get dominated
by disk head motion.  GCR tape recording is a very reliable and proven
technology.  One major advantage of the TA78s (and any other tape or disk
drive which emulates DEC products) is that system disk backups are easily
done and can be restored using Standalone Backup.  Consider if you use
a WORM drive which requires a special driver; you must still make provisions
to save your system disk on tape or disk such that Standalone Backup can
restore your system disk in case of ultimate "oops".  This is, I think,
the major problem with devices like the Megatape or ExiStore (I think
this is the name of the recently announced 8mm tape which can store
- get this - 2048 MB!).  We are planning to add a TU81+ to our LAVC to
replace TK50 backups for just this sort of reason (currently the LAVC
has dual RA81s, soon to be a full set of 4).

WORM disks would be nice.  However, vendors seem to be concentrating on
making WORM disks look like read/write magnetic disks in terms of the
on-disk file structure and system access.  A better and probably cheaper
solution for WORM backups would be to make the WORM drive look like a
magnetic tape.  One other thing about WORM drives; their data transfer
rates are SLOW, on the order of 200KBytes/sec for writing.  This is
considerably slower than current tape technology.


-Frank Nagy
-Fermilab Research Division EED/Controls
-FNAL::NAGY.HEPNET or NAGY@FNAL.Bitnet