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Cybernetics
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parity information until the failed drive is regenerated. This can cause degradation in
application program performance for both reads and writes.
This is the most versatile RAID level, and thus recommended for application, database,
and file servers, and also ideal for email, news and WWW servers.
RAID 50
– This RAID level is a combination of RAID 5 and RAID 0, and requires a mini-
mum of six disks installed, in order to provide striping to RAID 5 subarrays. This provides
better transfer rate speeds than RAID 5 alone, especially with write speeds, but not as
high as pure RAID 0. RAID 50 is recommended for critical small file applications requiring
higher transfer speeds.
RAID 5 + Hot Spare
– The RAID 5 + Hot Spare configuration is a RAID 5 array with a
dedicated “Hot Spare” drive.
In essence, the RAID 5 array operates as described previously, however, there is an
additional Hot Spare drive that is set up as a standby drive for use as a global spare (i.e.,
immediately available for use by any RAID 5 array). The Hot Spare drive sits idle awaiting
a failure in the RAID 5 array. In the event of a failure, the Hot Spare drive will take over for
the failed drive automatically and the RAID 5 array will not suffer performance degrada-
tion.
The Hot Spare drive configuration is recommended for a critical RAID 5 array where a
drive failure in the array should not cause downtime.
SCSI Cable
– For use with the miSAN-V-Series, a shielded cable having a VHDCI 68-pin
male connector for an LVD bus or an HD 68-pin male connector for an HVD bus.
SCSI Terminator
– A device attached to the end-points of a bus network or
daisy-chain
.
The purpose of the terminator is to absorb signals so that they do not reflect back down
the line.
Striping
– A data storage technique used in most RAID levels. Striping is a method of
mapping data across the physical drives in an array to create a large logical drive. The
data is subdivided equally into consecutive segments, or “stripes,” that are written
sequentially across the drives in the array. Each stripe has a defined size or depth in
blocks.
A striped array of drives can offer improved write/read performance compared to an
individual drive if the stripe size is matched to the type of application program
supported by the array:
•
In an I/O-intensive or transactional environment where multiple concurrent requests
for small data records occur, larger (block-level) stripes are preferable. If a stripe on
an individual drive is large enough to contain an entire record, the drives in the array
can respond independently to these simultaneous data requests.
•
In a data-intensive environment where large data records are stored, smaller (byte-
level) stripes are more appropriate. If a given data record extends across several
drives in the array, the contents of the record can be read in parallel, improving the
overall data transfer rate.
System Policy
– The policy specified by the “Host vs. job I/O policy” setting, which deter-
mines the priority of
host I/O relative to job I/O.
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