Hitachi Storage Arrays

Hitachi Shadow Image

Shadow Image uses local mirroring technology to create and maintain a full copy of any volume in the Storage Array.

Why Secondary Copy?

SI copies are used as backups, with secondary host applications, Data Mining, for testing and other uses.

Working Procedure of Shadow Image:

First select a volume that you want to duplicate. This becomes the Primary Volume (P-VOL).

Identify another volume to contain the copy. This Becomes the Secondary Volume (S_VOL).

Associate the P-VOL & S-VOL, Perform the initial Copy.

(Here the Source Volume is called as P-VOL & the destination Volume is called as S-VOL)

Once the initial copy is in progress the P-VOL is available for Read/Write.

Once the copy is completed the volumes are in paired state. After the copy is completed, subsequent write operations to the P-VOL are continuously copied to the S-VOL.

The P-VOL & S-VOL are remains paired till they are Split.

After Split S-VOl data is consistent and usable. It is available for read/write access by secondary host applications.

We can Pair the volumes by resynchronizing the updated data from P-VOL to S-VOL and S-VOL to P-VOL.

Each P-VOl can be paired with up to three S-VOls, means you can create three pairs with one source volume.

You can Pair with each S-VOL with a Second Level S-VOls.

Each S-VOL can be paired up to two secondary level S-VOLs. It means totally nine S-VOLs can be available for one P-VOL. These Secondary level S-VOLs are called as Cascaded Pairs.

Supported RAID levels --- RAID 1, RAID 5 and RAID 6.

Pair Topology Type : select the boxes that match your configuration.

Pair Topology

Pair Creation

In Split Type, you have the option of splitting the pair once it is created. Select one of the following:

1. Non Split: Does not split the new pair.

2. Quick Split: The new pair is split prior to data copy so that the SVOL is immediately available for read and writes I/O. Any remaining differential data is copied to the S-VOL in the background.

3. Steady Split: Splits the new pair after all differential data is copied to the S-VOL.

In Copy Pace, select the pace at which data is to be copied, Slower, Medium, or Faster.

Processing speed and system performance are affected by the pace you select; you see slower speed and better performance with Slower, faster speed but more impact to performance with Faster.

Pair Operations:

Create Pairs

Split Pairs

Resync Pairs (forward/reverse)

Suspend Pairs

Delete Pairs

Pair Status Descriptions:

SMPL : The volume is not assigned to a pair. The storage system accepts read/write for “SMPL” volumes that are not reserved.

SMPL (PD) : The pair is being deleted. Pair operations are not allowed in this status. Upon deletion, the status changes to “SMPL”.

P-VOL access: Read/write disabled

S-VOL access: Read/write disabled

COPY (PD)/ COPY: The pair creates initial copy is in progress. The storage system accepts read/write to the P-VOL but stops write operations to the S-VOL.