Raid Implementations - Acer HDS AMS200 Reference Manual

Acer hds ams200 server: reference guide
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5.2

Raid Implementations

The AMS200 subsystem supports RAID0, RAID1, RAID 5, RAID 6, and RAID1+0. RKAJAT does not
support RAID0.
RAID0 group stripes data across all disk drives in the group to attain higher throughput.
There is no sparing disk drive function with this configuration.
Notes on Using RAID0:
When a failure occurs in a disk drive, data cannot be restored internally within the
disk array because RAID0 has no redundancy of data; therefore, although the host
receives an error message, the data is left in its current state.
Unlike with an independent disk drive, error block management (assignment of
alternative block for the independent disk drive with the Reassign Blocks command)
is not done. Therefore, when a RAID0 disk drive becomes inaccessible due to a
failure, all the LUs in the RAID0 configuration including the failed disk drive become
inaccessible. Restoration of user data with backup data is essential after replacing
the failed disk drive.
Do not allow RAID0 to coexist with the other RAID group; do not form a group with
two or more RAID0 systems. An example = (4D + 1P) × 2 + 2D.
Each time a failure occurs in a RAID0 disk drive, data that cannot be written into the
disk drive (pinned data) is accumulated in the cache.
When the amount of accumulated data exceeds a certain value, a write I/O
instructed to the other RAID group cannot be accepted and the system goes down.
(In this case, restoration of user data and resynchronization of a file system using
the backup data are required for the entire subsystem; therefore, the time
necessary for recovery is lengthy.)
Do not adopt the RAID0 configuration to its fullest extent. Consider the above notes
when building the configuration.
RAID1+0 groups provide data redundancy like RAID1 by copying all the contents of two
disk drives to another pair. Different from RAID1, data striping is performed for a
maximum of 16 sets of two disk drives.
RAID1 array groups consist of at least two disk drives in a mirrored configuration. Data is
mirrored across the groups of two adjacent drives. The stripe consists of two data
chunks.
RAID5 applies 2 to 15 data disks and has a parity disk which performs the data stripping.
RAID 6 applies 2 to 28 data disks, and has two parity disks performing the data stripping.
Configuration with two parity disks provides redundancy that can sustain two point
failures.
96
Chapter 5 Functional and Operational Characteristics

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