On Thursday, Oct 23, 2003, at 14:12 Australia/Sydney, Adrian Hicks
wrote:
Hello,
Is there any formula to work out that is the best size for TSM DB
sizes on a SAN ??
Say if we had 100 Gb DB would you re-create it into 10 X 10 Gb volumes
or 50 x 2Gb vols, all on JFS2 etc, ?? Is there any logic not to have
large DB's on a SAN rather than smaller ones.
This is for an TSM 5.1.x on AIX 5.1
Regulars here may know my thoughts, and disagree with some of them, but
here goes:
You want to keep the disks busy, and service as many I/Os per second as
possible. I'd recommend about 3-4 DB volumes per physical disk. Given
you are talking SAN, this is where things get a little hazy. TSM has a
mutex lock on each DB volume, which limits the number of I/Os in flight
to each DB volume to 1. My testing on a 4-disk RAID 5 SAN attached HDS
indicates 1 I/O thread to one LUN gives about 100 I/Os per second.
Running
around 6-8 I/O threads can give up to 1000 I/Os per second. So in this
particular case, 6-8 (or preferably even more) DB volumes per parity
group
is the way to go. Note that all of this is talking random I/O, exactly
what
the TSM DB gets.
As to filesystem, my preference is raw volumes. For AIX, even raw hdisks
would be possible, although using raw LVs may be less confusing to the
newbies. If you want to use filesystems, my recommendation would be
JFS2,
mounted with the "dio" (O_DIRECT) flag. Note that I haven't tested this
with TSM, but it runs great with Oracle. The advantage is that the I/O
bypasses the AIX buffer cache (minperm/maxperm for JFS, maxclient for
JFS2,
CDFS and NFS), and hence paging is less of an issue, as is CPU usage
(the
AIX kernel thread "lrud" has much less to do). It also means vmtune
settings
are much less of an issue. TSM can manage its own cache better than AIX.
Have a look at
<http://stix.homeunix.net:8080/thoughts/tsm-perftune.html>
for other thoughts - mind you, this page needs a few updates with my
recent
discoveries.
Cheers,
--
Paul Ripke
Unix/OpenVMS/TSM/DBA
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