i get daily .OST report of users.

right now all 300 users .OST file is being saved on a file server from where the script runs and send the report.

i have been noticing the available size like (outlookE drive ) where ost files are stored is decresing drastically by 5 to 10 gb almost every alternate day

for ex. on 1/1/2019 it was 60 gb free but on 1/5/2019 it is 41gb free, though i see only 1 duplicate ost.

i also compared each ost of user with the previous report, i see very marginal difference in ost file  size of users comparing 1/1/2019 to 1/5/2019

so what is causing drastic decrease
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WORKS2011Managed IT Services, Cyber Security, BackupCommented:
right now all 300 users .OST file is being saved on a file server...
I don't believe it's recommended to use PST or OST files on a shared drive because of read and write limitations that can cause corruption and performance issues.

I would run Treesize (it's free) and see where the large files are located. Make sure to turn off hidden files.

I expect you'll find log files which will report what's going on.
pramod1Author Commented:
It is not me who decide I am simply asking a question kindly provide ur answer to that
WORKS2011Managed IT Services, Cyber Security, BackupCommented:
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WORKS2011Managed IT Services, Cyber Security, BackupCommented:
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Serge FournierAnalyst ProgrammerCommented:
If outlook is open for a user, the backup will not have access to the OST file, since it is open exclusively when outlook is open

So maybe your backup delete each file in the destination if it cannot access the original? Or generate a 0 k size ost at the destination

And, no, you do not need to copy a OST file on a share (i do not call this a backup, because it's just a copy), because, the OST file IS a copy from the mail server. So instead of copying the ost file, you should backup the mail server.
Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
Seriously, if there are only OST files on that share, someone did not do homeworks. It is absolutely useless to have a OST file (in particular for Exchange) on a network drive, it is a cache of centrally stored emails. You use OST files to have offline access to your mails, and speed up searches and other operations taking place locally (first) then.

However, the "why does my used space grow" question is posed very often. TreeSize Professional can do that - you create a XML report, later compare against a recent scan, and get the differences. But you need to pay for it ;-).
Other ways to get  a comparison is by running PowerShelll scripts to record the current file layout, and then compare the results with a difference tool (or the PS compare-object cmdlet).

Since you checked each OST file already, the most probably reason for growth is that there is no OST file gowring fast, or you made a mistake (which is likely). As has been said above, there might be hidden files, log files or something else stored. On the other hand, if you look at OST file growth: 300 users á 10 MB growth per user = 3 GB, so even "marginal" growth results in bigger total figures.

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Mal OsborneAlpha GeekCommented:
Keeping all OST files on a shared network drive is certainly a weird configuration. No idea why anyone would do that, and it WILL cause problems.

The growth rate you are seeing is not all that excessive. Assuming 5-10Gb every second day, that works out to around 8 - 16Mb per user per day.  Each user, sending or receiving 20-40 emails with an average size of 400Kb would do it.

With the config that you have in place, you will need a HEAP of space, and if resources are limited, quite a bit of management overhead. You could do the following:
1. Sort OSTs by last modified date, and try to determinate if those not changed in the last week or month are actually in use. Old ones can of course be deleted.
2. Sort by size. For the largest .OST files, take a look inside the mailboxes, determine why the user has so much email, and see if some can be deleted. Often users keep a lot of junk; if you order their inbox and sent items by email size within Outlook,  it is often pretty simple to get rid of significant amounts of garbage.
3. Once users have deleted whatever junk they can, compare .OST sizes with mailbox sizes indicated on the Exchange server or Office 365. .OST files generally only grow, they do not automatically shrink. ie, if Bill has 40Gb of email, cached in a 40Gb .OST file, and he manages to clean up and reduce this to 10Gb, the .OST file will still be 40Gb, including 30GB of unused "White space". Getting rid of white space can be done within Outlook, via "compacting".
4. Consider applying some restrictions to reduce mailbox size. Capping mailboxes at a manageable maximum size, and reducing maximum message sizes could be helpful, but of course will impact users.

If none of that is effective, then you will just need to provide adequate hardware for your weird configuration.  I generally size hardware assuming a 5 year lifespan. Given this, you need to arrange around 6Tb of disk space.
Thomas Zucker-ScharffSolution GuideCommented:
Just from an application perspective, I think that WinDirStat is far easier to use and understand than TreeSizePro.
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