7065DS3KBasicConfig.fm
Draft Document for Review August 30, 2007 12:59 am
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IBM System Storage DS3000: Introduction and Implementation Guide
drive from the array. In addition, only arrays with RAID levels 1, 3, 5 and 10 can be protected
against enclosure loss. RAID 0 array has no redundancy, so enclosure loss protection is not
possible.
Figure 4-7 displays an example of an array protected against enclosure loss. The array
consists of four physical drives, marked
Drive1, Drive2, Drive3
and
Drive4
. As you can see,
each drive is in a different enclosure.
Figure 4-7 Enclosure loss protection
4.1.3 Hot spares
Even though disk drives are becoming increasingly more reliable, disk failures can occur. To
protect your data in case of a drive failure, you should primarily use a redundant RAID level,
for example RAID 1, 10 or 5. This way, your data will remain intact should a hard drive fail.
However, the array will then operate in a degraded state, until the failed disk drive is replaced
and data reconstruction completes on the new disk drive.
To assure as high availability as possible, we strongly recommend to use hot spare drives.
Under normal circumstances, the hot spare drives do not participate in any array. When one
of the disk drives fails, the host spare will automatically be used as a replacement drive. Data
reconstruction onto the hot spare will take place immediately. When reconstruction finishes,
the array will again be in a fully operational status and the hot spare will become a member of
the array.
Depending on your configuration, it might be wise to use more than just one hot spare. In
small DS3000 configurations with a relatively low number of disk drives, one hot spare might
suffice. But for larger configurations, we recommend to define several hot spares.
When defining hot spare drives, you need to consider the drive size. For example, if you use
a mixture of different disk drive sizes in your arrays, the hot spare drive size must be large
enough so that it can effectively replace any of the drives.
4.1.4 Storage partitioning
The DS3000 subsystem can provide storage access to many host servers. Access to the
RAID controllers is shared among the attached host servers. However, the actual logical
DS3000
EXP3000
EXP3000
EXP3000
Drive 1
Drive 2
Drive 3
Drive 4
