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Daily snapshot will be taken at every 00:00. Weekly snapshot will be taken every
Sunday 00:00. Monthly snapshot will be taken every first day of month 00:00.
Rollback
The data in snapshot can rollback to the original virtual disk. Please follow the procedures.
1.
In Snapshots tab, selects a snapshot. And then click
▼
-> Rollback.
2.
Click OK to apply.
CAUTION:
Before executing rollback, it is better that the disk is unmounted on the host computer
for flushing data from cache.
Snapshot Constraint
Snapshot function applies Copy-on-Write technique on virtual disk and provides a quick and efficient backup
methodology. When taking a snapshot, it does not copy any data at first time until a request of data
modification comes in. The snapshot copies the original data to snapshot space and then overwrites the
original data with new changes. With this technique, snapshot only copies the changed data instead of
copying whole data. It will save a lot of disk space.
Create a data-consistent snapshot
Before using snapshot, user has to know why sometimes the data corrupts after rollback of snapshot.
Please refer to the following diagram.
When user modifies the data from host, the data will pass through file system and memory of the host (write
caching). Then the host will flush the data from memory to physical disks, no matter the disk is local disk
(IDE or SATA), DAS (SCSI or SAS), or SAN (fibre or iSCSI). From the viewpoint of storage device, it cannot
control the behavior of host side. This case maybe happens. If a snapshot is taken, some data is still in
memory and not flush to disk. Then the snapshot may have an incomplete image of original data. The
problem does not belong to the storage device. To avoid this data inconsistent issue between snapshot and
original data, user has to make the operating system flush the data from memory of host (write caching) into
disk before taking snapshot.
