Defrag required to reclaim space?

[blakey2]

Hi all,
I am hoping that this question is fairly academic for one of you.

If you hit the good 'ol 16GB limit and exchange goes off line. You need to defrag it, hope it 'finds'/consolidates the free space and decides to let you restart services.

If then the next day, you delete a couple of gig from users mailboxes, do you need to defrag the database again to realise the space? If no then how does it find the extra space, which enables you to bring it back online?

Cheers - Chris.

 

[zbnet]

Exchange (Standard) will start any store that has a priv.edb of less than 16GB in size. Exchange will stop any store when the priv.edb would exceed 16GB in size if it completed writing the current transaction into the database.

Both of the above sentances are truisms. But if you have a running store, and you delete a couple of GBs of data, the physical size of the priv.edb still wont reduce until you do another offline defrag. But you don't necessarily need to reduce the size of priv.edb, the store will run happily enough with priv.edb just under the limit.

So long as you have deleted all references to the email you have deleted from the store (which is kind of hard to do sometimes with single instance storage), then Exchange will mark the email as expired. If you have any Deleted Item Retention period set, it waits for this many days, and then the overnight db maintenance will mark the space as 'white' (ie reusable). Overnight db maintenance (make sure you have it scheduled - but not at the same time as you're trying to backup the store!) is also the process that does an online defrag, shuffling all the data into pages at one 'end' of the file and all the white space to the other 'end' of the file. When the overnight online defrag has completed a pass, it writes a 1221 log to the Application event log (one for each edb file) to report on the quantity of white space in the db.

White space will always be used to write new data into a store if it exists. Only when there is insufficient white space to store the new data does Exchange try and increase the size of the priv.edb file.

So the short answer is, so long as your store is reporting whitespace in the 1221 events, your store should be safe and keep on running no matter how close it is to the size limit.

BTW, prevention is better than cure - always try and prevent Exchange Standard from reching the 16GB limit, it will make your life a lot easuer.

 

[Zelandakh]

Seconded. Nicely but zb.

Repeated defrags are a bad idea. If the store is running, leave as is - as long as you have enough white space to cope. If not, defrag won't help and only Enterprise will save you.

Time for an upgrade to Exchange 2003 ready for SP2 with its 75GB standard limit?