June 28, 2016 /
0 comments /
in General Support /
by Jacob Allred
If your production database is larger than 500 Gb, I’d like to take a moment to talk about a potential ticking time bomb that might be present in your production environment so that you have the tools necessary to disarm it before it detonates.
Extreme file fragmentation + Small disk allocation size = Disaster
The VHS uses ESE as its database technology, the same database technology used in Microsoft’s Exchange Server. This database technology allows for massive sizes but NTFS has some gotchas that can cause issues when any one file becomes very large and is experiencing fragmentation.
First let’s get a primer on how files are stored within an NTFS volume. Go read these two articles from Microsoft:
Now that we’re acquainted with NTFS, lets discuss this limitation and how it affects large database files such as the VHS.
What does this failure look like once it occurs?
As of right now, there isn’t a SVCMON point that will be able to give you insight into this problem. You may have to use windows utilities to determine the root cause of the issue (such as CONTIG.exe to determine the number of fragments). Run contig with this “-a” switch it will analyze the fragmentation count of the file you are investigating. If contig reports ~1.5 million fragments then you are dangerously close to the failure condition.
How do we avoid hitting this issue? There are a couple options:
If you choose option 2 be aware that you will need to:
Copy and pasting files from one volume to another will also make them contiguous, so any fragmentation the file is experiencing will be addressed as part of that operation.
We hope that this will help you to be familiar with issues that can arise from large databases and the NTFS file system. If you have any questions about this issue or need assistance investigating please contact us at email@example.com
*updated to reflect additional info requested by Mike McElveen
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