APPENDIX
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Online RAID Level and Stripe Size Migration
For those who wish to later upgrade to any RAID capabilities, a
system with Sans Digital online RAID level/stripe size migration allows
a simplified upgrade to any supported RAID level without having
to reinstall the operating system.
The RAID subsystems 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 RAID
subsystem. 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 recon-
figured 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 process,
the volume sets being migrated are accessed by the host sys-
tem. In addition, the volume sets with RAID level 1, 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 mi-
grating state to (midegraded) state. When the migra-
