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Introduction
Hitachi AMS 2100/2300 Storage System Hardware Guide
RAID implementations
The AMS 2100/2300 supports RAID 0, RAID 1+0, RAID 1, RAID 5, RAID 6,
or an intermix, as described below.
Table 1-10: RAID Implementations
RAID
Level
Description
0
RAID 0 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:
•
When a failure occurs in a disk drive, data cannot be restored
internally within the disk array because RAID 0 has no data redundancy.
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 RAID 0 disk
drive becomes inaccessible due to a failure, all the logical units in the
RAID 0 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 RAID 0 to coexist with another RAID group. Do not form
a group with two or more RAID 0 systems, for example (4D + 1P) × 2 +
2D.
•
Each time a failure occurs in a RAID 0 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 will not be accepted and the system
will crash. In this case, restoration of user data and resynchronization of a
file system using the backup data are required for the entire array. The
recovery time for this procedure can be quite long.
•
Do not adopt the RAID 0 configuration to its fullest extent. Consider
the above notes when building the configuration.
1+0
1
1. RAID 0+1 is described in place of RAID 1+0 in some places in this document.
However, it has the same meaning as RAID 1+0.
RAID
1+0 groups provide data redundancy like RAID 1 by copying all the
contents of two disk drives to another pair. Different from RAID 1, data
striping is performed for a maximum of 16 sets of two disk drives.
1
RAID
1 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.
5
RAID 5 uses from 2 to 15 data disks, and has a parity disk performing the
data striping.
6
RAID 6 uses from 2 to 28 data disks, and has two parity disks performing
the data striping. Configuration with two parity disks provides the
redundancy that can sustain two points failures.
Summary of Contents for AMS 2100
Page 20: ...xx Preface Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 28: ...1 8 Introduction Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 50: ...1 30 Introduction Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 176: ...5 58 Installation Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 240: ...7 58 Configuration Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 278: ...10 6 Upgrading the firmware Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 292: ...B 6 Regulatory information Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 304: ...Index 4 Hitachi AMS 2100 2300 Storage System Hardware Guide ...
Page 305: ...Hitachi AMS 2100 2300 Storage System Hardware Guide ...