Glossary - Sun Microsystems StorageTek 9985V Manual

Term
Array
Array hot-spare
Asymmetric volume
access
Auto-sensing
Back-End Director
Block or block size
Cache
Cache hit
Chunk
Clean data
Concatenation
Control path
Controller pair
Controller tray
Controller unit
Copy-On-Write
(COW)
CRC error checking
DAS
Data path
Dedicated hot-spare
Dirty data
Disk
Just the Facts
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Glossary

Storage system consisting of trays and controller units. Storage system
consisting of a minimum of one controller unit. Also includes one or more slots
to house disks drives.
Disk that serves as a hot-spare within an array. A reserve disk that can be made
available to all virtual disks within an array.
A storage access method that provides multiple data paths to the same volume,
but allows only a subset of data paths at a time to be active.
Automatically determining the type of device connected (N-port, NL-port,
F-port, FL-port, or Fabric) and adapting the port speed and interface protocol to
match.
A pair of array control processors (ACPs).
Amount of data sent or received by the host per I/O operation. Atomic
read/write operation to/from a disk. Size of data unit that is striped across disks.
DRAM-based staging area used to provide higher performance to applications
for reads and writes. During reads, the controller unit tries to keep the latest and
most often accessed data in cache and also tries to pre-stage cache with future
data during sequential accesses. For writes, cache is used to provide delayed
writes to the disks. This delays the parity calculations and disk writes during
RAID 5 operations. More optimization and advanced staging algorithms thus
provide better performance.
Read or write request for data that is already in cache. Therefore, a request can
be serviced without needing to go to disk.
A quantity of information that is handled as a unit by the host and disk device.
Any read data or write data that has been committed to disk. In other words, a
copy of data that is safely on disk.
Sequentially mapping blocks on disks to a logical device. Two or more extents
can be concatenated and accessed as a single logical device. Add extents to an
existing volume.
The communications path used for system management information. Generally
provided as an out-of-band connection over Ethernet.
Pair of controller units servicing a particular tray or group of trays.
A tray with one or more installed controller units.
The intelligence card that manages RAID functions and fail-over characteristics
for an array or tray, or group of trays.
The process that Sun StorageTek 9900 Copy-on-Write software uses to preserve
point-in-time data when new data is written to disk. With each write, the system
preserves the old data in snapshot reserve space, so that it can re-create the
volume as it existed at the time of the snapshot.
Checking for frames that have been corrupted (some of the 1 bits changed to 0
bits, and vice versa), due to noise or collision.
Direct attach storage. Storage directly attached to servers or hosts (as opposed
to SAN storage where storage is attached to a network of storage devices).
The path traveled by data packet — between the host processor and the disk.
Disk that serves as a hot-spare to one, and only one, virtual disk in an array or
tray.
Write data that is in cache and has been acknowledged to the application host,
but which has not yet been committed to disk.
Physical entity that stores data (as compared to a virtual disk, which is a logical
grouping of disks or storage extents).
October 2007
Definition
177