Hi
First off, the number of spindles is not the only important factor. What kind
of disk are you using for the database? Do you have a disk cache for read /
write caching or is it JBOD in a machine?
Second off, to aquire maximum performance on a limited amount of spindles, I
suggest you use the mirroring feature within TSM and use parallellism. That
way, TSM will have the ability to read / write from multiple DB copies
containing the same information. It will also protect you from a partial write,
something that hardware mirroring / striping wont. Remember to use TSM's
shadowing in thise case or the partial write protection is gonna be lost if you
use parallellism.
To say what is the best setup for your particular environment isnt that easy
since we're missing out factors such as size of database, amount of memory
available for DB cache (bufferpool). How you treat the log will also be an
impacting factor in your setup.
In the case of DB, RAID-5 isnt always a bad choice. DB writes/read are quite
random. And the % of reads compared to the % of writes will also affect any
performance gain you will get from using striping (RAID-0) since striping will
give you a performance gain from writes, but in the case of a TSM DB not when
it comes to reads.
In my opinion, 4 physical disks are abit low if it comes to holding both
primary and secondary copies of the database and still have enough DB volumes.
According to TSM performance redbooks, 6-8 DB volumes (in some cases I have
seen number saying 8-12, but that obviously depends on the size of your
database) is a good setup for gaining a good performance, but with only 4
spindles, you're limited to only 4 (placing more than 1 copy on each spindle is
gonna reduce performance if this is JBOD disks). Therefore, depending on the
size of your database, I would say going with 2 main DB copies and 2 secondary
DB copies would be a good choice.
If the disksubsystem you're using doesnt have write/read cache, you might
consider placing the volumes on a JFS-2 filesystem instead of using raw devices
(which I usually use when I have a disksubsystem with a large amount of memory
cache) to gain advantage of AIX's file system cache. You will however in this
case have to adjust the MINPERM and MAXPERM settings (you adjust these settings
with the vmo command) for how much memory the system is allowed to use for
filecaching to adjust your system to work optimal. Remeber not to kick up both
your DB bufferpool and the filesystem cache since if these both start fighting
for memory, you'll end up getting your bufferpool data or filesystem cached
paged instead, which will reduce performance.
Best Regards
Daniel Sparrman
________________________________________
Från: ADSM: Dist Stor Manager [ADSM-L AT VM.MARIST DOT EDU] för Oscar
Kolsteren [Oscar.Kolsteren AT INGDIRECT.CO DOT UK]
Skickat: den 19 februari 2009 09:04
Till: ADSM-L AT VM.MARIST DOT EDU
Ämne: Re: 4 spindles for db: best performing setup
Hi Michael,
I have a similar environment and created two RAID 0 lun's of 2 disks
each. The mirroring is done in TSM itself.
I'm more interested in what segment size people use on the disks and if
a certain pp size is recommended for a volume group under AIX.
Good luck
Best Regards,
Oscar
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Michael Green
Sent: 18 February 2009 20:23
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] 4 spindles for db: best performing setup
You are given 4 spindles to place TSM DB on them.
How would you set them up to squeeze maximum performance for DB?
1. Dedicate each spindle for a DBC (result: 3 DBCs, one spindle left
out, nevermind)
2. Create RAID 0 out of each pair of disks. Place a DBC on each RAID
(result: 2 DBCs on two separate RAID 0)
3. Create RAID 1 out of each pair of disks. Place a DBC on each RAID
(result: 2 DBCs on two separate RAID 1)
4. Create RAID 5 out of all spindles. Place one DBC on the RAID
(result: 1 DBC on RAID5)
Notes:
a. There is no RAID 0+1
c. Wasted space is not a concern
--
Warm regards,
Michael Green
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