Size of .PST and .OST files

[jmt356]

I once read that if a .PST grows to be larger than 5 GB, the risk of corruption goes up. Is the same true of .OST files?

If so, how can I go about archiving the items in an .OST file? Is it the same as creating an archive for a .PST file--i.e., create a new .PST file to serve as the archive and drag older emails and calendar items to the archive? Will this cause the items that are archived to be removed from both the local computer and the corresponding MS Exchange Server?

On a related note, Outlook takes a long time to load. Does a 4.5 GB .PST file and an 18 GB .OST file have anything to do with this?

[JoeP]

You can setup an archive for an account using an OST file just the same as setting up any other archive. The archive file will be a PST file. You can manage it the same way. Either run auto-archive or manually move items.

The size of your various OST and PST files will impact how long Outlook takes to initialize.

Joe

[HansV]

See Recommended pst-/ost-file size vs. Maximum technical size.

[jmt356]

What will happen to the emails on the MS Exchange Server if I move them from my Inbox to an archive folder? Will they be deleted from the Server? Or will they remain and then be replicated into my Inbox after I have removed them from my Inbox to my archive folder?

[HansV]

If you move an item from Exchange to a .pst file, it will be removed from Exchange, and as far as I know from your offline file (.ost) too.

[JoeP]

SInce the .OST file is a copy of what is on Exchange it will be removed from the .OST too. That may not be instantaneous it depends on your send/receive settings.

Joe

[HansV]

Thanks for the confirmation, Joe.

[jmt356]

Something very strange has happened with my MS Exchange files.

I initially had a single .OST file at 17.8 GB.

I then archived my emails from 2014 and earlier. I now have a 11.3 GB .OST file, a 9.17 GB .PST archive file and a 2.39 GB .PST archive file, which add up to 22.86 GB. How is it possible that by archiving emails in a 17.8 GB .OST file, I now have an .OST and two .PST files whose combined total space exceeds that of the original .OST file? As I understand, I have only been moving around files rather than creating new ones.

[HansV]

There's a lot of overhead - search indexes for example, so I'm not surprised at all that the three files combined are larger than the original one.

[PJ_in_FL]

Just because you moved an email -- or a lot of emails -- from the .OST file doesn't mean the space is freed up and the file shrinks. That space is unused and can only be recovered by compacting the OST, if that's possible. I know it's possible to compact PST files.

If not, then just accept the OST is not a space-efficient file format. After all, it's a MS proprietary format, so expecting rational behavior may be asking too much....

[jmt356]

Well, I am still left with my original problem; I have only managed to get my .OST file down to 9.75 GB from 17.8 GB.

Is anyone aware of whether an OST file can be compacted / compressed?

[Leif]

Try Reduce the size of Outlook Data Files (.pst and .ost) - Outlook

[Rudi]

    
In addition to Leif's link, see:

1. How to compact PST and OST files to eliminate deleted item space in Outlook
2. Shrink your pst-file or ost-file after cleanup with Compact Now

[jmt356]

I just archived emails into a 1.6 GB PST file. I would have expected the 4.2 GB OST to have gone down in size. Logically, it should have gone down by the 1.6 GB corresponding to the new PST.

However, there was no change to the size of the OST after I removed 1.6 GB of emails. However, I followed the steps to compact the OST file and it has now gone down to 3.1 GB. So removing 1.6 GB of emails reduced its size by 1.1 GB.

[DaveA]

Remember that these PST/OST files contains ALL of the data from Outlook, calendar, contacts and etc.
So if you have a large mount of these then it will still be large.