Set minimum allocation size for dynamic disks

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Spizmar
Posts: 2
Joined: 5. Nov 2018, 22:30

Set minimum allocation size for dynamic disks

Post by Spizmar »

The core problem is NTFS error 655, which occurs when a file with attributes of some type allocated to the file fragments gets "too" fragmented.
In the VM it shows up as write errors, in the host (obviously windows) as error 655.

While 1MB chunks may seem OK at first, since my VDI has grown to 72GB, that is up to 72K fragments, and my VM is really having serious issues.
If I could set the minimum allocation size to 500 MB, or 1 GB, it would keep this problem from occurring as fast in future dynamic VDI files.

Look at it as a trade-off between dynamic and static disks.
mpack
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Joined: 4. Sep 2008, 17:09
Primary OS: MS Windows 10
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Re: Set minimum allocation size for dynamic disks

Post by mpack »

Minor typo: I think you mean error 665, not 655. Also this error code is not NTFS specific (you'd hit the same error when writing to offset 4GB in a file on a FAT32 volume).

Interesting, I hadn't realized that fragmentation could ever be a problem on an SSD (mentioned in your other post). And in truth I'm still struggling to see how it could ever arise in practice on an NTFS volume. VDIs do NOT grow haphazardly, they grow when some guest process writes to areas of the disk not previously used, the probability of which should decrease as the drive fills up.

There has to be a missing element for your scenario, such as constantly working with a host disk fill factor >90%. Also you'd have to be running a guest app that is continuously writing to new areas of the disk: perhaps a background defrag task?
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