Concerned about VHD file growth on clones

RandyBCD

We started using SQL Clone exclusively for our lower environments and spec'd things out based off documentation provided by RedGate, discussions on various threads, etc...  We have seen a very large growth rate in the VHD file unfortunately and much greater than what we expected.  We are at a point now that the use of SQL Clone provides less value than what was sold to us initially.   Are there configurations or changes we can make overall to reduce the change rate in the VHD file to reduce overall disk consumption?

praveen_d

This link explains a possible reason for clone to inflate.

https://documentation.red-gate.com/clone2/troubleshooting/common-issues/the-files-behind-the-clone-have-grown-to-be-very-large

RandyBCD

Unfortunately that link did not help, we don't have any maintenance plans running on this instance and have confirmed that.  We continue to see large VHD file growth where we see no benefit in using the SQL Clone product for any type of disk savings.

owen.hall

Hi Randy,

As you'll know, clones are differencing disks, and will grow when something writes to their data files. The usual culprit is SQL Server, which makes its own decisions about what to write to attached data files, and when. That can make diagnosing these kinds of issues tricky.

I've got a few diagnostic questions:

• Do clones grow on their own if you don't write to them? (E.g. they're just created, with no modification template, and are left to sit there.)
• Do clones grow on their own if they're made from images without any modifications?
• If you've been seeing growth in clones based on an image from a live database, what about clones based on an image from a backup file? (Or vice versa if you've been making images from backup files?)
• Do you have any clones that don't grow by themselves? Is there any pattern there?

Thanks!

Owen

John_Zabroski_wam

The simplest way to diagnose this is to use DMVs and look at indexes with high write counts, since DMVs reset since last reboot or when the db was last created.  As long as you did not reboot between the time you created the clone, then the writes will lead you to exactly what you are doing to balloon the db size.