ADSM-L

Re: ADSM/Backint parallel backups on an SP

1997-04-02 09:22:51
Subject: Re: ADSM/Backint parallel backups on an SP
From: Jeff Renicker <jrenicker AT VNET.IBM DOT COM>
Date: Wed, 2 Apr 1997 09:22:51 EST
In message <9703312039.AA11119 AT alssun.adc DOT com>, Jim Bootz
<bootz AT ADC DOT COM> writes
>Recently, we attempted for the first time to do parallel backups to three 3590

>tape drives in a 3494 robotic library across an SP switch and failed with
>numerous "TCP/IP connection" failures. Similar parallel backups across
ethernet
>worked fine, but were much slower than a switch. We also had success using
just
>two drives and the SP switch. Has anyone else had this experience? Is this a
>matter of tuning (our 'no' settings are considered optimal according to the
>latest information on SP tuning)? Or, are we expecting too much?

We had the same problem and contacted the support center.  Apparently the
device driver for the SP switch (TB3), not the High Performance switch (TB2),
now does it's own buffer handling.  If the buffer size is too low then ADSM
suffers from time-out problems when backing up across the switch.  Raising
the buffer size fixed our problems.

To check the buffer size issue the command: lsattr -E -l css0
and check the values for "spoolsize" and "rpoolsize".  These specify the number
of bytes to allocate for send and receive pools.  These values default to 512K.
The support center recommended values of 10M to 15M for ADSM backups.

We set our spoolsize and rpoolsize to 10M each this past weekend and ADSM is
now running fat, dumb, and happy.

You change the values using this command:
/usr/lpp/ssp/css/chgcss -l css0 -a spoolsize=10485760 -a rpoolsize=10485760

(this is the command we used to change the pools to 10M)

There are some caveats, though.  First, the spoolsize and rpoolsize values
MUST be the same on all nodes using the switch.  Apparently during an Estart
there is some hand-shaking between the adapters and the lowest values for
spoolsize and rpoolsize get propagated to all the nodes.  Second, since the
the buffers are at the device driver level, and are only obtained at boot time,
a reboot of all the nodes is required to change spoolsize and rpoolsize.

Hope this helps.

Jeff Renicker
IBM GLobal Services
e-mail: jrenicker AT vnet.ibm DOT com
voice: (330) 796-3984
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