Accusys ExaRAID GUI - Manual (Page 209)

Advanced Functions
5-36
• Restoring by Snapshots
Users can online restore a primary volume to one of its snapshot volumes.
After the restore, the contents of the primary volume immediately
become the current image of data of the selected snapshot volume,
and the primary volume is accessible. A backward synchronization task is
started in the background to copy data of segments from the secondary
volume and spare COW volume to overwrite the differential data on the
primary volume. During the restoring, the I/O access to the primary
volume and the other snapshot volumes can still be processed normally,
but only after the restoring is done, new snapshots can be created again.
• Online Volume Expansion
The capacity of primary volume, secondary volume, and spare COW
volume can be expanded without interfering with the operations of the
snapshot volumes. After the capacity expansion operation is done for a
volume or a logical disk, the new capacity can be automatically
recognized and utilized by the snapshot functions. You may use this
feature to allocate limited space for secondary volume and expand the
secondary volumes later when more hard disks are available.
5.4.3 How to Use Snapshots
• Overview
To make the most use of the snapshot function, proper planning and
configuration is of essence. Below is a list of related tasks grouped into
three phases:
Phase 1: Planning
1. Identify the source volumes that need to have snapshots.
2. Define how many snapshots will be taken and how long they will
exist.
3. Allocate the disk space and RAID attributes of the secondary
volumes.
4. Allocate the disk space and RAID attributes of the spare COW
volume.
Note
1. The total maximum number of volume pairs is 64/16 for 512MB/
1GB (1GB/512MB) memory installed.
2. The total maximum number of snapshot volumes is 512
3. The maximum number of snapshot volumes per primary volume is
32
4. The maximum capacity of primary/secondary/spare COW volume
is 16TB
5. The minimum capacity of secondary volume is 32MB
6. The minimum capacity of spare COW volume is 128MB
7. The maximum number of spare COW volumes is 128