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date: 28 Feb 2007 07:39:11 -0800,
group: microsoft.public.exchange.design
back
Re: Rate of change in an Exchange database
On Feb 28, 9:29 pm, "John Fullbright [MVP]"
<fjohn@donotspamnetappdotcom> wrote:
> Unless you're doing something extremely unusual, like delivery to PST or all
> POP clients, that figure sounds very suspect. I typically see more like
> 3-5% at the item level. It's important to distinguish that from the block
> level however. I have seen aggressive Online Maintenance (online defrag
> represents the majority of changes) schedules cause block level changes on
> the order of 40%. Do be aware that MS recommends that Online Defrag
> complete once every two weeks. If you schedule less agressively to meet
> this target, then the block level changes are on the order of the item level
> changes.
>
> John
>
> wrote in message
>
> news:1172677151.480155.33320@8g2000cwh.googlegroups.com...
>
>
>
> > We recently met with some consultants to discuss up and coming
> >Exchangedesign work. I was very interested to hear that within a
> > database (in a normal working day) 80% of that file willchangein a
> > day, even if there is little actual mail/changecaused by user
> > activity.
>
> > Can anyone clarify this or point me maybe to an official document?
> > Many thanks, H.- Hide quoted text -
>
> - Show quoted text -
Hi there, thanks for your reply. We are not doing anything unusual
with our databases, but as my other reply states I am very interested
in getting the source from this quote. Hence firstly I needed to know
if this was a known figure within the Exchange community (I'd not
heard it before, and so sure I would have) before going back to the
consultancy. As we are looking at database copies across the SAN,
then we are talking block level I guess. We have an online defrag
once a week, during the weekend, we don't have many users (3k) split
across two Exchange boxes. Happy to hear any thoughts. Thanks,
Hutton.
date: 1 Mar 2007 01:55:56 -0800
author: unknown
Re: Rate of change in an Exchange database
1. If there are no changes, then online defrag has nothing to move.
2. The first 10 steps of online maintenance (purging indices, marking
items, etc) creates a great deal of IO, but impacts relatively few blocks.
Snapping and shipping the change delta is very efficient for this type of
IO.
3. From Jeremey Kelley's Blog
http://blogs.msdn.com/jeremyk/archive/2004/06/12/154283.aspx "The intention
for online defragmentation is to free up pages in the database by compacting
records onto the fewest number of pages possible, thus reducing the amount
of I/O necessary. The ESE database engine does this by walking the database
metadata (information in the database that describes tables in the database)
and for each table, visit each page in the table and attempt to move records
onto logically order pages. If you have an understanding of BTrees, we start
at the furthest page to the right and begin compressing records to the left
most page. This does not necessarily mean the pages are in order, but the
movement is from a logical perspective." If you make a lot of changes, and
complete a defrag several times a day, you could see high rates of block
level change. The source for the 40% figure for online defrag was
http://www.microsoft.com/technet/technetmag/issues/2006/10/FailoverClusters/default.aspx
If reduce the aggressiveness of online defrag, you quickly drop from 40% or
so to 5 or 6% or lower.
wrote in message
news:1172742956.795866.177980@s48g2000cws.googlegroups.com...
> On Feb 28, 9:29 pm, "John Fullbright [MVP]"
> <fjohn@donotspamnetappdotcom> wrote:
>> Unless you're doing something extremely unusual, like delivery to PST or
>> all
>> POP clients, that figure sounds very suspect. I typically see more like
>> 3-5% at the item level. It's important to distinguish that from the
>> block
>> level however. I have seen aggressive Online Maintenance (online defrag
>> represents the majority of changes) schedules cause block level changes
>> on
>> the order of 40%. Do be aware that MS recommends that Online Defrag
>> complete once every two weeks. If you schedule less agressively to meet
>> this target, then the block level changes are on the order of the item
>> level
>> changes.
>>
>> John
>>
>> wrote in message
>>
>> news:1172677151.480155.33320@8g2000cwh.googlegroups.com...
>>
>>
>>
>> > We recently met with some consultants to discuss up and coming
>> >Exchangedesign work. I was very interested to hear that within a
>> > database (in a normal working day) 80% of that file willchangein a
>> > day, even if there is little actual mail/changecaused by user
>> > activity.
>>
>> > Can anyone clarify this or point me maybe to an official document?
>> > Many thanks, H.- Hide quoted text -
>>
>> - Show quoted text -
>
> Hi there, thanks for your reply. We are not doing anything unusual
> with our databases, but as my other reply states I am very interested
> in getting the source from this quote. Hence firstly I needed to know
> if this was a known figure within the Exchange community (I'd not
> heard it before, and so sure I would have) before going back to the
> consultancy. As we are looking at database copies across the SAN,
> then we are talking block level I guess. We have an online defrag
> once a week, during the weekend, we don't have many users (3k) split
> across two Exchange boxes. Happy to hear any thoughts. Thanks,
> Hutton.
>
date: Thu, 1 Mar 2007 07:10:55 -0800
author: John Fullbright [MVP] fjohn@donotspamnetappdotcom
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