Large amount of space disk %default/merged.*.dat

We encounter some problem of space disk in our exchange architecture.
I can see a folder at this place which take a lot of place:
E:\Exchange_2013\Mailbox\Mailbox Database 0459122375*.Single\ms\%default\part.00002200.merge

It take up to 20% of all storage i got.
I want to know if i can delete them without risk and how can i prevent this to happened

My setup is two exchange servers 2013 installed on 2012 server with a dag on two databases.

I have two disk partitions and exchange installe one the data part.

Thanks for your help
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Casey WeaverManaged Services Windows Engineer IIICommented:
They are exchange server search indexes, and they grow to about 20% of the database size. If you look at the Exchange sizing guide, these search index sizes are included in the proper sizing.

Make sure you're up to date on your cumulative updates. There was a bug where they would grow over 50%.
WaycomAuthor Commented:
Thanks for the answer,
I also have this folder: E:\Exchange_2013\Logging\Diagnostics\DailyPerformanceLogs

Can i disable these logs and delete them?

Thanks for your help.
AmitIT ArchitectCommented:
What is your dB size and disk size?
WaycomAuthor Commented:
I have two DBs:
One of 259GB and the other 55GB.
My data partition is 430GB

Thanks for your help
Casey WeaverManaged Services Windows Engineer IIICommented:
I don't know if you ever got your solution, but there is this solution to clearing out the logs:

Due to the nature of the beast though, I would highly recommend expanding the disk, if that option is available. Messing with Exchange's natural processes is just not something I enjoy doing :).

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