ADSM-L

Re: poor performance

2006-08-21 15:47:30
Subject: Re: poor performance
From: "Allen S. Rout" <asr AT UFL DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Mon, 21 Aug 2006 14:43:01 -0400
>> On Mon, 21 Aug 2006 08:43:26 -0700, "Gill, Geoffrey L." <GEOFFREY.L.GILL AT 
>> SAIC DOT COM> said:

> To be more clear. The 4 D40's are a mixture of database, logs and
> disk pools. One VG for database, one for mirrored database and one
> for data storage pools.

Mkay; good. :)

What size disks?  were these the same disks as on your previous setup?

When I moved from 9G to 18G spindles for databases, I found that
having DB volumes fill the spindle blew my performance for ( I
inferred ) contention reasons.

You said 120GB; I'll presume that's available space.  Even with 36G
SSA, that's just 4 volumes, 4 threads with which DB work can be done.

For comparison's sake, with 316GB of aggregate available databse
space, I have 35 volumes defined, mostly on 18G spindles.

Now, I'm in a very different environment, 11 servers on that piece of
hardware.  But even so, you get the sense.  My largest single DB,
~70G, has 8 (mirrored) volumes.

I think it possible that you will see performance improvement if you
merely cut your DB volume size.  Don't go nuts, there's certainly a
performance trainwreck at the other side of the scale, too: dozens of
DB vols per spindle is Right Out.  But you might consider 2 or 3 if
you're at 36G, maybe even more if you're at 72.


> Four full D40's just for a database would be quite unnecessary.

Agreed, though I wasn't visualizing that; I was visualizing one JBOD
RAID (raid-0?) with LVs carved out for whatever purposes.


> No raid anywhere, all raw disk consisting of one LV per disk no
> matter if it is database, log or disk pool related.

Digression: strongly suggest RAID for the data pools.  5-disk RAIDs
seem to be good performance for SSA, and then you have a hot spare
1/drawer.

Pedantic comment: If you're doing LVM with unraided disks, I'm not
sure JBOD applies.  Isn't that a RAID term-of-art?

Gratuitous label:  things come in threes.


- Allen S. Rout

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