Areca ARC-1880 Series User Manual page 183

APPENDIX
Online RAID Level and Stripe Size Migration
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For those who wish to later upgrade to any RAID capabilities,
a system with online RAID level/stripe size migration allows a
simplified upgrade to any supported RAID level without having
to reinstall the operating system.
The RAID controllers can migrate both the RAID level and stripe
size of an existing volume set, while the server is online and
the volume set is in use. Online RAID level/stripe size migration
can prove helpful during performance tuning activities as well as
when additional physical disks are added to the RAID control-
ler. For example, in a system using two drives in RAID level 1,
it is possible to add a single drive and add capacity and retain
fault tolerance. (Normally, expanding a RAID level 1 array would
require the addition of two disks). A third disk can be added to
the existing RAID logical drive and the volume set can then be
migrated from RAID level 1 to 5. The result would be parity fault
tolerance and double the available capacity without taking the
system down. A forth disk could be added to migrate to RAID
level 6. It is only possible to migrate to a higher RAID level by
adding a disk; disks in an existing array can't be reconfigured
for a higher RAID level without adding a disk.
Online migration is only permitted to begin, if all volumes to be
migrated are in the normal mode. During the migration pro-
cess, the volume sets being migrated are accessed by the host
system. In addition, the volume sets with RAID level 1, 1E, 10,
3, 5 or 6 are protected against data loss in the event of disk
failure(s). In the case of disk failure, the volume set transitions
from migrating state to (migrating+degraded) state. When the
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