NEC NF2900-SR40E, Руководство пользователя

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10
2.2 Write Cache Feature
For RAID levels 5, 6, or 50, the performance of the disk array unit may decrease during the writing of
small amounts of data. This is because the previous data and parity data must be read to recalculate the
parity.
So, 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 the disk drive,
improving the performance.
In general, if the power is shut down before the data saved in the cache memory is written to the disk
drive, the data in the cache memory will be lost. To prevent this, the disk array unit provides a battery
backup to the power supply to retain data in the cache memory.
The backup time using the Battery Backup Unit is restricted as follows:
The backup time of the battery backup unit depends on the capacity of the installed cache memory and
the service period of the battery. The following table shows the backup time when two battery backup
units are installed and they are both fully charged.
The following conditions are imposed to make the write cache preservation feature effective:
„
Two controllers, one or more battery backup units, and power supplies for the battery backup unit
(PS0 for BBU0, PS1 for BBU1) are installed and operating normally.
„
The battery backup units are fully charged.
If any of the conditions are not satisfied, the write cache preservation feature will not work properly.
The batteries installed in the battery backup unit are fully charged for about eight hours.
If the battery switch on battery backup unit is not turned on, the battery backup unit does not operate.
Battery Back Up unit Service period
Cache memory capacity
2 .5 years or under 2.5 to 5 years
4GB 96H 48H
8GB 72H 36H
16GB 48H 24H
* The battery backup time can be maintained by replacing the battery at intervals of 2.5 years
(with charge).
* The life expectancy of a battery is 5 years. However, if the power on/off sequence is required
everyday, the batteries are exhausted faster. If so, the batteries should be replaced with
charge at intervals of 2.5 years.