Setting Up File Snapshot - Novell NETWARE 6-DOCUMENTATION Manual

Setting Up File Snapshot

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Novell Storage Services Administration Guide
The File Snapshot feature enables your backup utility to keep an original copy
of all data files. For example, when your system backs up or crashes at a time
when you are modifying a file, the file backup could contain both old and new
data. Snapshot captures the most recent closed copy of the file. This way, if
you lose data between the backup cycles, you still have a solid copy of the
previously saved file.
If you select File Snapshot on a volume, the backup utility copies all the meta-
data (owner, created date/time, modifier, etc.). During write requests, only the
data that is being written to is copied. NSS recognizes how to return the
appropriate data when read requests come in for the real file or the Snapshot
file.
Use the following NSS command at the server console to enable the File
Snapshot for a volume:
nss/FileCopyOnWrite=<volName>
or
nss/FileCopyOnWrite=all
To disable File Snapshot, enter the following:
nss/NoFileCopyOnWrite
After you set up File Snapshot on your volumes, you need to deactivate the
volumes. Then you need to activate and mount the volumes again to ensure
there are no open files without a snapshot.
To open a snapshot file for backup, you need to set a bit in the requested rights
parameter in addition to READ_ACCESS_BIT. This bit is 0x04000000. It is
defined in the NSS header files as zPR_READ_ACCESS_TO_SNAPSHOT.
The default setting for File Snapshot is when your file system receives an open
for write request, it will wait for the backup open to close the file. If you want
to return an error, the backup open should also set the deny the write bit.
To get information on a snapshot file, use the getInfo command. Any getInfo
call that returns packed information with the RNewStyle bit set in the info
mask is supported. You need to set an additional bit 0x20000000 in the
information mask. This bit is defined at RNSSInfoOnSnapshot in NSS header
files. Both open and getinfo calls require the bit for requested rights and the
bit for additional info mask.