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I read about VSS here. According to the article , VSS takes a backup of the entire volume. Where does this backup of the Volume get stored ? If its on the volume itself then its pretty unsafe right ?
Does it work like Hardware Snaps ?
Dhiwakar Ravikumar
Posted 2014-10-31T04:16:43.890
Reputation: 1 551
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To maintain efficiency, shadow copies are indeed stored on the same volume. That’s just how snapshots work. It’s the same with ZFS.
The copy-on-write method creates shadow copies that are differential rather than full copies of the original data. Like the clone method of creating shadow copies, the copy-on-write method can produce shadow copies using either software or hardware solutions. This method makes a copy of the original data before it is overwritten with new changes, as shown in the following table. When a change to the original volume occurs, but before it is written to disk, the block about to be modified is read and then written to a “differences area”, which preserves a copy of the data block before it is overwritten with the change. Using the blocks in the differences area and unchanged blocks in the original volume, a shadow copy can be logically constructed that represents the shadow copy at the point in time in which it was created.
(Emphasis mine)
This means that initially, a shadow copy is just a flag. As data starts to change, changed data is backed up to different locations on the disk so the original data stays available.
Daniel B
Posted 2014-10-31T04:16:43.890
Reputation: 40 502
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VSS snapshots are stored under the folder System Volume Information.
The folder contains information that casual interference could cause problems with proper system functioning. Here are some of the things kept in that folder.
- Information used by the Volume Snapshot Service (also known as "Volume Shadow Copy") so you can back up files on a live system.
magicandre1981
Posted 2014-10-31T04:16:43.890
Reputation: 86 560
So am I right in assuming enabing VSS on my Computer can slow it down because of latency caused by having to copy the block about to be modified to "differences area" or "reserve space" (in NetApp Filer Terms). Also what if I've modified all the blocks in my volume ? Then there will be an extra copy of each block of the Volume on the Volume.... So a 10GB volume would now have 20GB of data ??? – Dhiwakar Ravikumar – 2014-11-01T05:10:19.277
Yes, although the “slowdown” only occurs once for each block. If you overwrote everything then naturally it would use that much space. I don’t see what’s so surprising about this. ;) – Daniel B – 2014-11-01T13:34:17.243
Shadow Copies are not necessarily stored on the same volume: https://docs.microsoft.com/de-de/windows-server/storage/file-server/volume-shadow-copy-service#where-is-the-diff-area-located https://docs.microsoft.com/de-de/windows-server/storage/file-server/volume-shadow-copy-service#how-is-the-diff-area-location-determined
– Thorsten Schöning – 2019-09-13T13:27:34.283