Promise Technology 15110 user manual Ranges of Disk Array Expansion

Chapter 7: Technology Background

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Important

•The Target disk array may require more disk drives than the Source disk array

•If the Target disk array requires an EVEN number of disk drives but the Source disk array has an ODD number, ADD a disk drive as part of the migration process

•You cannot reduce the number of disk drives in your disk array, even if the Target disk array requires fewer disk drives than the Source disk array

•RAID 1 (mirroring) works with two drives only. Only a single- drive RAID 0 disk array or a single-drive JBOD can migrate to RAID 1. Other RAID Levels use too many drives to migrate

•You cannot migrate a disk array when it is Critical or performing activities such as Synchronizing, Rebuilding and

PDM

Ranges of Disk Array Expansion

There are limitations to how large you can expand a disk array, depending on the size of your current disk array.

The current SCSI and Fibre Channel HBA cards and PC Operating Systems support a 10-byte LBA format. This means that a disk array can have up to 4 billion address blocks or sectors.

Multiply the number of blocks by the sector size to find the capacity of a disk array:

4,000,000,000 blocks x 512 bytes per sector = 2,048,000,000,000 bytes of data for a 2TB drive.

Note that you cannot change the size of the sectors nor can you increase the number of address blocks above 4 billiion.

As a result, there are range limits imposed upon disk array expansion as shown in the table above. For example:

•You can expand a 2.5 TB disk array up to 4 TB

•You can only expand a 1.9 TB disk array up to 2 TB

See the chart on the next page.

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