Ranges Of Logical Drive Expansion - Promise Technology VTRAK 15200 User Manual

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Ranges of Logical Drive Expansion

There are limitations to how large you can expand a Logical Drive, depending on
the size of your current Logical Drive.
The current iSCSI HBA cards and PC Operating Systems support a 10-byte LBA
format. This means that a Logical Drive 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 Logical
Drive:
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 Logical Drive expansion as
shown in the table above. For example:
• You can expand a 2.5 TB Logical Drive up to 4 TB
• You can only expand a 1.9 TB Logical Drive up to 2 TB
See the chart on the next page.
• The Target Logical Drive may require more disk drives than
the Source Logical Drive
• If the Target Logical Drive requires an EVEN number of disk
drives but the Source Logical Drive has an ODD number,
ADD a disk drive as part of the migration process
• You cannot reduce the number of disk drives in your Logical
Drive, even if the Target Logical Drive requires fewer disk
drives than the Source Logical Drive
• RAID 1 (mirroring) works with two drives only. Only a single-
drive RAID 0 Logical Drive or a single-drive JBOD can
migrate to RAID 1. Other RAID Levels use too many drives to
migrate
• You cannot migrate a Logical Drive when it is Critical or
performing activities such as Synchronizing, Rebuilding and
PDM
Chapter 7: Technology Background
Important
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