Re: IO Bottleneck

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Thanks, Al! That was very informative...

Next week I will move the logs, and I'll let you guys know how it went.

"Al Mulnick" escribió:

Just to point out: it's not the space as much as the separate spindles that
you're after. That separation is one of the best performance related
investments you can make. As was explained earlier and as you've noticed,
Exchange is very disk dependent. Very. Several things can be done to help
reduce the impact, but at the end of it all, the io has to be handled at
some point.

Understand that there are several different things going on for the life
span of a message submission/delivery/retrieval event (all of these can be
going on at the same time.) A lot of it is going to utilize the disk.
There will be several different io types i.e. sequential write, random
read/write, and sequential read are primarily what you'll have to account
for. Putting them all on the same physical spindles can have a serious
impact on performance due to disk contention. Of those, the one io type most
noticable to users is the sequential write of the log files. This is an
artifact of the two-phase commit database technology employed by the jet
engine. You want that to occur, trust me. But if that write to the log file
is slowed, then store gets blocked and your users may notice it.

So what can you do about it? For starters, you can optimize the disk
subsystem so that these events don't impact one another nearly as much.
Separating io types is the way to achieve that and by far putting the log
files on their own separate set of write-optimized physical disks is a low
cost, and easy way to do that. Using raid5 for log files is not recommended
for that reason. raid 10 or 1 depending on the sizing information is often
recommended and used with great success.

Another thing you can do is use cached mode for your users. This has a
bigger impact when first fired up, but the user is less impacted later.

You may also want to check out your global catalog servers. If the majority
of your users are OWA users, then the impact on the server should be much
different than what you describe and disk should be less of a concern in
many cases. Your case may be different, but generally speaking. You should
also take the advice posted and find out what the message patterns are: are
there a lot of large blobs being submitted? Are there other applications
affecting you? etc.

My $0.04 anyway.

<jamestechman@xxxxxxxxx> wrote in message
news:1156557888.578680.31840@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Yes log files grow in increments of 5MB. 73GB is overkill for logfiles.
36GB is the smallest HD you can get for the HP servers, which will
suffice.

James Chong

Ariel wrote:
Thanks, I will try to collect some data with exmon.

One thing I've noticed is that my log files never grow above 5MB each...
35MB total... is that normal? Should I really use two 73GB disks to store
just 35MB?


"Simon Walsh" escribió:

Run an EXMON on the server.
Look for unusual user activity in real time.
Start with the worst offenders. Turn their Outlook client off. Any
change?
What version of Outlook are they using? Have you installed all the
latest
fixes for those clients?
Are their bunches of users that are sending/receiving the exact same
amount
of bytes/second?
Just a few tips

/Simon.


"Ariel" <Ariel@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:0B83F4E4-B6EB-45AD-8AFF-DD46FEF3C47F@xxxxxxxxxxxxxxxx
My databases are 36GB in size.
I am not running blackberry.
Most of my clients use OWA.
I am not sure how to determine if the users have desktop search, I saw
a
couple of ones, but it's probably 5 users in total.
I am not running indexing or message tracking.

PTA says that user activity is unusually high.

Thanks for all your help

"jamestechman@xxxxxxxxx" escribió:

You're absolutely correct, this server should be able to support
substantially more than 300 users. Let's try to get some more info as
to the source of your I\O bottleneck in terms of user IOPS. How big
are
your user's MB? Are you running Blackberry? Are your clients running
any desktop search engines, ie. google desktop search, yahoo desktop
search... Are you doing any Exchange indexing? What other
applications
are running on the server?

James Chong
MCSE M+, S+, MCTS, Security+
msexchangetips.blogspot.com


Ariel wrote:
Bummer, I really don't know what I'm gonna do now... probably
change
the
delay for the RPC dialog so I don't get so many complaints, until I
am
able
to buy a new server. What really bothers me is that this server,
properly
configured, should be able to service much more than 300 users...

"John Fullbright [MVP]" wrote:

Write cache could remorve 1 IO operation out of 4 for RAID 5.
Instead of
defining write performance as P*N'/4, you could descibe it as
P*N'/3.

For your 4 drive RAID 5 array using 10K drives, your current
write
performance would be something like 85*3/4 or 61 IOPS. Adding
the
write
cache could, depending on controller architecture, change that to
85*3/3 or
85 IOPS. I doubt that, in practical terms, it would make much
difference.



"Ariel" <Ariel@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:C812D79F-A273-4DA4-908A-79514F8E5096@xxxxxxxxxxxxxxxx
John:

Thanks for your response. The way you describe is exactly how I
would
design
a new server. However, this is our only exchange production
server,
and I
need to improve performance as much as possible without
reinstalling it.

So, would adding the battery backed write cache improve
performance
in a
significant way? And would I be better of moving something else
to
the
logs
disk, say, the smtp queue or temp dirs?

"John Fullbright [MVP]" escribió:

At a minimum, you should have a mirror for the OS, a mirror
for
the logs,
and a mirror (or RAID 10) for the databases. I'd hazard a
guess
that the
write times on the the RAID 5 array far exceed 20ms.


"Ariel" <Ariel@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:F0839239-546B-4AA9-8B55-5B0E7A4DC986@xxxxxxxxxxxxxxxx
I have recently become the administrator of an Exchange 2003
Server.
These
are the server specs:

HP Proliant DL380 G3
Dual Xeon 2.8GHz
2GB RAM
Smart Array 5i Controller with 64MB and read-only cache
4 x 300GB Ultra320 10K Hard Drives in a RAID 5 array

I have been assigned the task to investigate a possible
bottleneck,
since
users were seeing the RPC dialog frecuently. I ran the
Performance
Troubleshooting Analyzer, and of course, the results
indicated a
disk
bottleneck.

The server has room for 2 more hard drives. I tried adding a
73GB disk,
and
using it for the database logs, then ran the PTA again, and
now
the
report
says that I have a disk bottleneck in all the roles that
remained on
the
primary array.

I am going to add another 73GB disk to make a RAID 1 array,
and
move
the
logs anyways, but I was wondering if I should transfer
another
role to
that
new volume.
I am also considering buying an upgrade for the controller
to
add 128MB
of
battery-backed write cache, if it would help.

I would appreciate any advice you have to offer.

Regards,

Ariel.














.

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