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 I love deadlines. I like the whooshing sound they make as they fly by. -- Douglas Adams
