Online Raid Level And Stripe Size Migration; Online Volume Expansion - Areca ARC-1110 User Manual

INTRODUCTION

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 simplified upgrade to any supported RAID level without having
to reinstall the operating system.
ARC-11xx/12xx 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 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 capacity and
retain fault tolerance. (Normally, expanding a RAID level 1 ar-
ray would require the addition of two disks). A third disk can be
added to the existing RAID logical drive and the array can then
be migrated from RAID level 1 to 5. The result would be parity
fault tolerance and double the available capacity without tak-
ing 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 volume 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 levels 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 migrating state to (migrating+degraded) state. When the
migration 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 flexible
option is for the array to concatenate an additional drive into the
RAID set and then expand the volumes on the fly. This happens
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