backing up large filesystems

[Charles Hornig <Hornig@STONY-BROOK.SCRC.SYMBOLICS.COM>]

    Date: Tue, 20 Jun 89 15:03 PDT
    From: shirley.pa@Xerox.COM

    Are there better solutions to backing up a large filesystem than 40 megabyte
    cart tapes?  We now have ~20 tape full dumps and expect to double that soon.

    One possibility I'm looking into is using RTAPE and a Sun to back up to a 2
    gigabyte video cartridge.  Does anyone have experience with this?

I have a lot of experience doing this (to an XL400 instead of a Sun).

Make sure that you use RTAPE over TCP and not over CHAOS.  (With the
Sun, you won't have much choice.)

You will be very disappointed in how much data fits on a tape and in the
dumping speed.  The reason is that the LMFS dump format uses file marks
heavily and file marks are very expensive on the 8mm drive we use
(Exabyte).  They take up as much space as 2Mbytes of data.

This last problem will be fixed in ECO #2 to Genera 7.4, which
introduces a new dump format which is better suited to modern tape
devices.  Unfortunately, to use the new format over RTAPE requires an
enhancement to the server side.  That means you can use the new format
over RTAPE to an XL400 running the ECO, but not to a Sun unless you make
the equivalent change to its server.

With this change, things are pretty exciting.  I did a complete dump of
a 2GByte file system over RTAPE to an XL400 in 19 hours without manual
intervention.