ArrayMasStor J Series User’s Manual
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1.5
Write Back Cache Function
When used in RAID Level 5, the write operation for small data blocks causes a data bottleneck. This
is because, before it can write the new data, the ArrayMasStor must read the old data and parity,
which are needed to generate the new parity
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. This phenomenon, which is called the write penalty,
impairs performance when the host computer accesses the ArrayMasStor in a random write pattern.
The ArrayMasStor uses a large buffer as a write-back cache to compensate for the write penalty
problem. When data is acquired into the cache buffer by a ‘write’ command issued by the host
computer, the ArrayMasStor returns a ‘complete’ command to the host computer. The ArrayMasStor
gathers the small amounts of write data to the cache buffer and writes this data onto the drives at one
time.
When shutting down the ArrayMasStor using the power switch on the front panel, the ArrayMasStor‘s
firmware detects the power switch status, flushes the data in the cache to the drives, and then turns off
the power. When powering down from the AC line, a ‘synchronize cache’ command must be sent
from the host computer to the ArrayMasStor before the power is turned off. Failure to use the
‘synchronize cache’ command can result in data loss.
IMPORTANT !
Push Power Switch to turn off except for emergency. Turning
off by pulling out Power Line Cord may cause data loss in the
cache buffer.
Plugging AC power cord can’t be POWER-ON condition of ArrayMasStor J series.
IMPORTANT !
It is strongly recommended that an interruptible power
supply (UPS) be used to avoid data loss when the power
line is unstable and power outrage happens.
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This is called “Read Modify Write”.