April 28, 2008 at 4:13 pm
Why you cannot create snapshots on FAT32 file system or RAW partitions?
April 28, 2008 at 9:42 pm
Database snapshots use a feature of the NTFS file system that not available with FAT32/RAW file systems.
Whilst I don't claim to understand exactly what NTFS is doing, it is something to do with sparse files. When you create the snapshot, SQL asks NTFS to allocate a file that "could be as big as" the MDF/NDF's in the database but initially only needs to be (from memory) 64k. As data changes on a page in the database, the old image of the page is written to the snapshot file. If a page is not changed there is no need for the snapshot to store the page. Hence, the small initial allocation of space for the snapshot since it initially contain a bit of meta data.
It is my understanding that you cannot ask FAT32/RAW file systems to allocate just a part of a potentially large file.
I think that this is being done because, you don't really want to wait for the allocation of the full file sizes before you actually need them - hence, the creation of a database snapshot is really quite quick
April 29, 2008 at 2:47 pm
ok, happycat59, thank you for your answer 🙂
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