9track on 3b2

[Lyndon Nerenberg]

nickerso at bdofed.UUCP (b) writes:


>	Has anyone else had any experience with the 9track on a 3b2?  Our
>contacts at AT&T say that the throughput should be much higher.  It seems
>that the drive is stopping and starting as it writes (an indication that
>the buffering can't keep up with the drive???) which means it has to back up
>so that it can get the tape to the right speed at the right time.  Not exactly
>a time saver!

Our current config is a 3b2/600 tied to a 3b4000 (which has the 9track).
We RFS mount /dev/{rmt,rSA} from the 4000 onto the 600. I checked with
the operators, and they indicate a full backup of the 600 (about 500MB)
is taking about 16 hours.

The problems here are manyfold. The prime culprit is the 9track, and
its associated drivers. Physical throughput to the drive is bad at
the best of times, and I'm convinced the driver is doing nothing to
help out. I've run the same drive off a Sun 3/280 and made the thing
STREAM at 6250 during backups. If you can't get the drive out of washtub
mode ...

RFS is also no screaming hell. A lot of the problem in our case is the
painfully slow ethernet interface on the 3b4000. We're lucky to get
40K/sec through the wire doing ftp's, let alone RFS traffic.

Savecpio is not know for writing huge blocks, either. I'm not sure
of the size it uses, but watching the tape wobble on the drive I
would guess no larger than 10K/block. I'll check the source and see
what the story is here.

Something you might want to try would be to dd 100 meg from the raw
filesystem over the wire to the tape drive. Time how long it takes,
the run it again with output to /dev/null on the remote. This should
give you an idea of how much of a hit you're taking from the tape.

>	Please, any comments or suggestions would be welcome.  Send me email
>or phone or whatever.

A comment: I guess you haven't seen what happens when you take a tape
error towards the end of your dump set :-)

Ever think about porting Berkeley dump? We have ...
-- 
Lyndon Nerenberg  VE6BBM / Computing Services / Athabasca University
    {alberta,decwrl,ncc}!atha!lyndon || lyndon at cs.AthabascaU.CA
        If everyone quit smoking, drinking, and buying gas,
               the nation would probably go bankrupt.