Shadow copies, Introduction to shadow copies, Difference file – Dell PowerVault 775N (Rackmount NAS Appliance) User Manual
Page 53: Shadow copies considerations
Shadow Copies
Dell™ PowerVault™ 77xN NAS Systems Administrator's Guide
Defragmenting a Volume Containing Shadow Copies
Shadow Copy service allows the creation of point-in-time copies of your NAS system's data volumes. Shadow Copy software
can be configured using the NAS Manager.
NOTE:
Shadow copies can be accessed through SMB and NFS shares. Shadow copies cannot be accessed through
HTTP, FTP, AppleTalk, or NetWare shares.
Introduction to Shadow Copies
A shadow copy is a point-in-time copy of a shared file or folder. If you change a file on the active file system after making a
shadow copy, the shadow copy contains the old version of the file. If an active file gets corrupted or deleted, you can restore
the old version by copying the file from the latest shadow copy or restoring a directory or file.
NOTICE:
Shadow copies are temporary backups of your data that typically reside on the same volume as your data. If
the volume becomes damaged and you lose your data, the shadow copy is also lost. Therefore, using shadow copies
should not replace performing regular backups.
Difference File
The Shadow Copies service stores changed data in a difference file. A difference file resides on each volume of your system.
You can use the NAS Manager to change the amount of space that is dedicated to the difference file.
Shadow Copies Considerations
When using shadow copies, note the following:
When the shadow copy difference file reaches the maximum number of shadow copies (64 copies per volume), the
system deletes the oldest shadow copy file.
Shadow copies are read-only. You cannot edit them.
Shadow copies are made of entire volumes. You cannot make shadow copies of individual files or folders.
NFS clients can access shadow copy data as read-only files.
If you add a volume and you plan to defragment that volume, format the source volume where you intend to enable
shadow copies with an allocation unit size of 16 kilobytes (KB) or larger. If you do not format the shadow copies
volume, defragmenting the volume can cause previous versions of files to be deleted.
NOTE:
If you use NTFS file system file compression on the source volume, you cannot use an allocation unit size
larger than 4 KB. Defragmenting the source volume causes the difference file to grow. If the difference file grows