Write Cache Feature - NEC Storage S1300 User Manual

Write Cache Feature

In a RAID 5 configuration, the performance of the disk array unit may decrease during
writing of small amounts of data. It is because the previous and parity data must be read
to recalculate the parity.
The disk array unit is equipped with cache memory. When write data is stored in the
cache memory, the disk array unit terminates the command processing and then writes
the data to disks for improving the performance.
Note:
battery backup unit. However, to ensure a higher degree of data
protection, it is recommended to use a UPS (uninterruptible power
supply).
In general, if the power is shut down before the data saved in the cache memory is
written to disks, the data in the cache memory will be lost. To prevent this, the battery
backup unit retains data in the cache memory.
The backup time is restricted as follows:
Three days (72 hours) in full charge status of both batteries
The following conditions must be satisfied to make the write cache feature effective:
Two controllers, one or more battery backup units and power supplies for the
battery backup units are installed (factory-set).
The battery backup units are fully charged.
If any of the conditions is not satisfied, the write cache feature does not work
efficiently.
The batteries installed in the battery backup unit remain fully charged for about eight
hours.
1-20 System Overview
The cache memory is subject to battery backup by the