Disk Latency

18 May 2006 12:57 PM

tmelvin

DWe've recently installed MOM 2005, and it's monitoring our Exchange Servers.
All is well, but we're getting regular alerts about Disk Latency. It states
Disk Write Latency > 20 msec. I've checked the server, and it's operating
withing spec's. The log shows:

PhysicalDisk: Avg. Disk sec/Write: 1 E: value = 3.38264998003905E-02. The
average over last 10 samples is 0.0338265

Is this normal for Exchange 2003? People are getting email, and there are no
delays...

Thanks in advance.

18 May 2006 2:49 PM

John Fullbright [MVP]

MOM uses for triggers the same griteria stated in "optimizing storage for
Exchange server 2003"; average latency no greater than 20ms and no spikes
lasting more than a few seconds over 50ms. You are seeing average latencies
of 33.8ms.

How are you disks configured?

Show quote

"tmelvin" <tmel***@discussions.microsoft.com> wrote in message
news:0BE11872-E6C0-417E-9AB2-6B6F775DC442@microsoft.com...
> DWe've recently installed MOM 2005, and it's monitoring our Exchange
> Servers.
> All is well, but we're getting regular alerts about Disk Latency. It
> states
> Disk Write Latency > 20 msec. I've checked the server, and it's operating
> withing spec's. The log shows:
>
> PhysicalDisk: Avg. Disk sec/Write: 1 E: value = 3.38264998003905E-02.
> The
> average over last 10 samples is 0.0338265
>
> Is this normal for Exchange 2003? People are getting email, and there are
> no
> delays...
>
> Thanks in advance.

18 May 2006 3:22 PM

tmelvin

System/OS Volume is RAID 1+0 and the DB/LOG vols are RAID 5.

Show quote

"John Fullbright [MVP]" wrote:

> MOM uses for triggers the same griteria stated in "optimizing storage for
> Exchange server 2003"; average latency no greater than 20ms and no spikes
> lasting more than a few seconds over 50ms. You are seeing average latencies
> of 33.8ms.
>
> How are you disks configured?
>
>
> "tmelvin" <tmel***@discussions.microsoft.com> wrote in message
> news:0BE11872-E6C0-417E-9AB2-6B6F775DC442@microsoft.com...
> > DWe've recently installed MOM 2005, and it's monitoring our Exchange
> > Servers.
> > All is well, but we're getting regular alerts about Disk Latency. It
> > states
> > Disk Write Latency > 20 msec. I've checked the server, and it's operating
> > withing spec's. The log shows:
> >
> > PhysicalDisk: Avg. Disk sec/Write: 1 E: value = 3.38264998003905E-02.
> > The
> > average over last 10 samples is 0.0338265
> >
> > Is this normal for Exchange 2003? People are getting email, and there are
> > no
> > delays...
> >
> > Thanks in advance.
>
>
>

18 May 2006 5:29 PM

John Fullbright [MVP]

"DB/LOG vols are RAID 5." is the source of your problem.

First, spilt the DBs and logs onto seperate volumes. Second:

RAID 5 is not acceptable in a modern Exchange environment. The reason is
the RAID 5 write penalty and read/write ratios in a modern Exchange
environment. A decade agao, back in the 5.5 days with Outlook 97 clients,
the read/write ratio was on the order of 8 to 1. RAID 5 has a write penalty
of P*N'/4. With 88% reads and only 12%, the write penalty was not as large
a factor when considering storage.

In today's Exchange 2003 Environments with Outlook 2003 client side caching,
the read/write ratio is more like 2:1 or 33% writes and the RAID 5 write
penalty becomes quite significant. You'll use many more spindles to reach
the same IOPS requirement using RAID 5 than you will with RAID 10. The
price you pay for the write performance increase using RAID 10 is space.

Go RAID 1/10.

Show quote

"tmelvin" <tmel***@discussions.microsoft.com> wrote in message
news:C9AF0D2B-A49D-4F21-8F50-F62F6E61CA88@microsoft.com...
> System/OS Volume is RAID 1+0 and the DB/LOG vols are RAID 5.
>
> "John Fullbright [MVP]" wrote:
>
>> MOM uses for triggers the same griteria stated in "optimizing storage for
>> Exchange server 2003"; average latency no greater than 20ms and no spikes
>> lasting more than a few seconds over 50ms. You are seeing average
>> latencies
>> of 33.8ms.
>>
>> How are you disks configured?
>>
>>
>> "tmelvin" <tmel***@discussions.microsoft.com> wrote in message
>> news:0BE11872-E6C0-417E-9AB2-6B6F775DC442@microsoft.com...
>> > DWe've recently installed MOM 2005, and it's monitoring our Exchange
>> > Servers.
>> > All is well, but we're getting regular alerts about Disk Latency. It
>> > states
>> > Disk Write Latency > 20 msec. I've checked the server, and it's
>> > operating
>> > withing spec's. The log shows:
>> >
>> > PhysicalDisk: Avg. Disk sec/Write: 1 E: value = 3.38264998003905E-02.
>> > The
>> > average over last 10 samples is 0.0338265
>> >
>> > Is this normal for Exchange 2003? People are getting email, and there
>> > are
>> > no
>> > delays...
>> >
>> > Thanks in advance.
>>
>>
>>

18 May 2006 5:54 PM

tmelvin

John,

Thanks for the information. I guess we need to determine how to go from 5 to
10 now...

Thanks again,

Show quote

"John Fullbright [MVP]" wrote:

> "DB/LOG vols are RAID 5." is the source of your problem.
>
> First, spilt the DBs and logs onto seperate volumes. Second:
>
> RAID 5 is not acceptable in a modern Exchange environment. The reason is
> the RAID 5 write penalty and read/write ratios in a modern Exchange
> environment. A decade agao, back in the 5.5 days with Outlook 97 clients,
> the read/write ratio was on the order of 8 to 1. RAID 5 has a write penalty
> of P*N'/4. With 88% reads and only 12%, the write penalty was not as large
> a factor when considering storage.
>
> In today's Exchange 2003 Environments with Outlook 2003 client side caching,
> the read/write ratio is more like 2:1 or 33% writes and the RAID 5 write
> penalty becomes quite significant. You'll use many more spindles to reach
> the same IOPS requirement using RAID 5 than you will with RAID 10. The
> price you pay for the write performance increase using RAID 10 is space.
>
> Go RAID 1/10.
>
>
>
> "tmelvin" <tmel***@discussions.microsoft.com> wrote in message
> news:C9AF0D2B-A49D-4F21-8F50-F62F6E61CA88@microsoft.com...
> > System/OS Volume is RAID 1+0 and the DB/LOG vols are RAID 5.
> >
> > "John Fullbright [MVP]" wrote:
> >
> >> MOM uses for triggers the same griteria stated in "optimizing storage for
> >> Exchange server 2003"; average latency no greater than 20ms and no spikes
> >> lasting more than a few seconds over 50ms. You are seeing average
> >> latencies
> >> of 33.8ms.
> >>
> >> How are you disks configured?
> >>
> >>
> >> "tmelvin" <tmel***@discussions.microsoft.com> wrote in message
> >> news:0BE11872-E6C0-417E-9AB2-6B6F775DC442@microsoft.com...
> >> > DWe've recently installed MOM 2005, and it's monitoring our Exchange
> >> > Servers.
> >> > All is well, but we're getting regular alerts about Disk Latency. It
> >> > states
> >> > Disk Write Latency > 20 msec. I've checked the server, and it's
> >> > operating
> >> > withing spec's. The log shows:
> >> >
> >> > PhysicalDisk: Avg. Disk sec/Write: 1 E: value = 3.38264998003905E-02.
> >> > The
> >> > average over last 10 samples is 0.0338265
> >> >
> >> > Is this normal for Exchange 2003? People are getting email, and there
> >> > are
> >> > no
> >> > delays...
> >> >
> >> > Thanks in advance.
> >>
> >>
> >>
>
>
>