Replicating Storage Units Using Clone

What is Clone?

Clone is a method of making a physical, point-in-time copy of a storage unit. EVM provides clone as a simple, single-click operation. All of the underlying StorageWorks CLI commands that are required for clone have been automated and incorporated into EVM.

When you specify the clone method in a job, EVM will automatically make duplicates, or BCV units, and mount them on a computer with the mount points that you specify. The BCV units are then available for a variety of purposes. You can also have the EVM job leave the BCV units unmounted, for example, as nearline backup.

 

Which ACS Versions Support Clone with EVM?

Versions 8.5F, 8.5L, 8.5P and 8.5S.

 

How Long Does Cloning Take?

The most important factors are the capacity and number of disks being normalized. Assuming a moderate I/O load on the StorageWorks HSG controller, and an adequate configuration of disks in the array, a replication rate of 60 GB per hour can be achieved.

 

How Does EVM Clone a Storage Unit?

For each unit to be cloned, EVM automatically checks the RAID level, determines the correct procedures, then searches the StorageWorks subsystem and selects free disks for the additional (BCV) mirror. EVM then copies the data and normalizes the disks in the mirror set. When normalization is complete, all members of the mirror set have identical data and EVM splits the additional (BCV) mirror from the mirror set.

EVM applies slightly different procedures, depending upon the type of source unit. You should review the differences in procedures outlined below and consider them when planning EVM jobs and storage configurations.

Source Unit is a Three-member Mirror Set (RAID 1, RAID 0+1). To achieve near instantaneous cloning with EVM, a source unit should be configured as a three-member mirror set and be fully normalized. In this configuration, EVM instantly splits the third member to create the BCV unit. This approach to instant cloning also applies to mirror sets with four or more members. See also Quick Clone.

Source Unit is a Two-member Mirror Set (RAID 1, RAID 0+1). EVM automatically adds a third member to the mirror set and normalizes the members. When the members are normalized, EVM splits the third member to create the new BCV unit.

Source Unit is Not Mirrored (RAID 0 and JBOD). EVM automatically creates a single member mirror set and then adds a second member. When the members are normalized, EVM splits the second member to create the new BCV unit.

 

Can I Clone RAID 3/5 Units?

No. Due to the presence of parity data, units that are configured as RAID 3/5 cannot be replicated by the clone method.

 

Can I Clone BCV Units?

No. EVM tracks the BCV units that it creates with each job and will not allow you to select one as a source for another job.