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INTRODUCTION
19
1.3.3.4 Online RAID Level and Stripe Size Migration
For those who wish to later upgrade to any RAID capabilities, a
system with Areca online RAID level/stripe size migration allows
a simplied upgrade to any supported RAID level without having
to reinstall the operating system.
The SATA RAID controllers can migrate both the RAID level and
stripe size of an existing volume set, while the server is on-
line 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 SATA
RAID controller. For example, in a system using two drives in
RAID level 1, it is possible to add a single drive and add capac-
ity 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
recongured for a higher RAID level without adding a disk.
Online migration is only permitted to begin, It all volumes to be
migrated are in the normal mode. During the migration process,
the volume sets being migrated are accessed by the host sys-
tem. In addition, the volume sets with RAID level 1, 1E, 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 mi-
grating state to (migrating+degraded) state. When the migra-
tion is completed, the volume set transitions to degraded mode.
If a global hot spare is present, then it further transitions to
rebuilding state.
1.3.3.5 Online Volume Expansion
Performing a volume expansion on the controller is the process
of growing only the size of the lastest volume. A more exible
option is for the array to concatenate an additional drive into the
RAID set and then expand the volumes on the y. This happens