Glossary–28
HSG80 Array Controller V8.7 Command Line Interface Reference Guide
Glossary
worldwide name
A unique 64-bit number assigned to a subsystem by the Institute of Electrical and Electronics
Engineers (IEEE) and set by DIGITAL manufacturing prior to shipping. Also called node ID
within the CLI.
write hole
The period of time in a RAID level 1 or RAID level 5 write operation when an opportunity
emerges for undetectable RAIDset data corruption. Write holes occur under conditions such as
power outages, where the writing of multiple members can be abruptly interrupted. A battery
backed-up cache design eliminates the write hole because data is preserved in cache and
unsuccessful write operations can be retried.
write-back caching
A cache management method used to decrease the subsystem’s response time to write requests
by allowing the controller to declare the write operation “complete” as soon as the data reaches
its cache memory. The controller performs the slower operation of writing the data to the disk
drives at a later time.
write-through cache
A cache management technique for retaining host write requests in read cache. When the host
requests a write operation, the controller writes data directly to the storage device. This
technique allows the controller to complete some read requests from the cache, greatly
improving the response time to retrieve data. The operation is complete only after the data to
be written is received by the target storage device.
This cache management method may update, invalidate, or delete data from the cache memory
accordingly, to ensure that the cache contains the most current data.
write-through caching
A cache management method used to decrease the subsystem’s response time to a read. This
method allows the controller to satisfy the request from the cache memory rather than from the
disk drives.