Re: Splitting our Exchange 2003 Ent Database
- From: "SW" <SW@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 11 Feb 2006 02:25:16 -0800
What perfmon disk counters can I run to get a baseline and what shoulr the
average around?
"SW" wrote:
what do you mean by spindles?.
"John Fullbright" wrote:
No.
Your log files, the most sensitive aspect of exchange IO from a user
visibility perspective, are competing with the OS, the page file, the system
temp directory, and the kitchen sink for IO. You need to have the logs on
an isolated set of spindles. You have 7 drives now. If you add an 8th and
reconfigure, you have a mirror for the OS, a mirror for the logs, and RAID
10 for the databases. RAID 10 with 4 spindles outperforms RAID 5 with 5
spindles.
Back in the Outlook 2000 days, read/write ratios used to be 3:1 or 4:1.
These days, with improvements in client side caching, they're more like 2:1.
RAID 5 performance is very assymetrical favoring reads over write by 4:1.
Write performance of RAID 5 quickly becomes a bottleneck when the read write
ratio is lower.
For example, you are currently saying you have a mirror for your logs and
RAID 5 for the databases.
For a mirror, max write performance = P*N/2. 85*2/2 = 85
For a 5 drive RAID 5 max write performance = P*N'/4 = 85*4/4 =85
For RAID 10 with 4 spindles, max write performance = P*N/2 = 170
Read performance for a 4 drive RAID 10 and a 5 drive RAID 5 are identical at
340
For a 2:1 read write ratio, RAID 5 Mixed performance = 252
For a 2:1 read write ratio, RAID 10 Mixed performance = 280 and this is
with one less spindle than the RAID 5 set.
For a 6 spindle RAID 10 Set:
Read = 510
Write = 255
Mixed = 421
Compare this to RAID 5 with 6 spindles
Read = 425
Write = 106
Mixed = 315
"SW" <SW@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:D8470751-D95E-4392-BB02-0430B475811C@xxxxxxxxxxxxxxxx
Sorry I was slightly wrong:
OS and transactions are on a Mirror. DB is on a RAID 5. It is using 2
RAID
cards one for each RAID. Any better?
"John Fullbright" wrote:
And the source of your problem is "5 disk as RAID 5 for DB and
transactions".
Let's say these ar 10K scsi spindles and every client uses ol2k3 cached
mode. Your read/write ratio is 2:1.
P=85 at a target 20ms IO
N=5
N'=4
Read perf = P*N' = 85*4 = 340
Write perf=P*N'/4=85*4/4=85
Performance = 340*.66+85*.33 = 224 + 28 = 254. With both the logs and
databases on the same physicals, you might get 100 users on there before
you
start seeing performance issues.
Loose the RAID 5, add a spindle and go with a mirror for the logs and
RAID
10 for the databases.
log performance will go to 128 IOPS, and database to 285. You will have
physical seperation of the log and database spindles.
"SW" <SW@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:9EB1C305-5DC4-4DB1-8A83-24C0C289E17A@xxxxxxxxxxxxxxxx
Out Exchange 2003 private DB is 100GB. We are getting users saying it
is
slow/sluggish sometimes. Ther is a Dual Xeon Dell Server, with 4GB
Mem, 2
disks as RAID 1 for OS, 5 disk as RAID 5 for DB and transactions.
Users
use
Outlook 2k and 2003.
We are thinking of creating a new storage group and putting a couple of
departments in it then doing an offline defrag of both DB's and the
public
DB. Would this provide better performance? If so why?
Thanks
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