Memory for disk arrays
RAID Arrays (depending on the mode of implementation of the controller) can be
presented as constructing software, and hardware. An example of the program can
serve as RAID OS Microsoft Windows NT Server 4.0, which is available software
implementation of RAID-0, -1 and even RAID-5 (Microsoft Windows NT Workstation
4.0 provides the only RAID-0 and RAID-1). However, this decision should be
viewed as extremely simplistic, not allowing the complete implementation of the
RAID array. Suffice it to say that when the program RAID whole load of
information on the placement of the floppy drive, by the calculation control
codes, etc. responsibility of the central processor, which certainly does not
increase productivity and system reliability. For the same reasons, there are
practically absent any service functions and operations to replace all the
defective drive, adding a new disk-yes, changes in the level of RAID, etc.
produced with the complete loss of data, with a total ban you completion of any
other operations. The only dignity of the program RAID - minimal cost. This
solution may be acceptable only if far-Go surplus computing power and low-server
load. Much more opportunities provides hardware implementation of RAID with
special RAID controller: -- specialized controller frees the CPU from the
central core operations with RAID, and the effectiveness of the controller is
all the more noticeable that the higher the level of difficulty RAID; --
controllers are typically equipped with drivers, allowing create RAID for almost
any popular OS; -- embedded controller BIOS and annexed management program
allows administrative system stratoru easily connect, disconnect or replace
floppies, members of the RAID, establishing several vat-RAID arrays, even at
different levels, monitor the status of the disk array, etc. "U" advanced
controllers, these operations can be made "on the fly", that is, not include
system unit. Many operations can be performed "in the background", that is,
without interrupting ongoing work, even remotely, that is, with any (of course,
if they have access), which work places; -- controllers can be equipped with a
buffer memory ( "Cache"), which are written the past few blocks, which is often
when you access the same files, allows significant increase ment speed disk
system.
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