Information Technology Reference
In-Depth Information
Virtual disk management systems implement one or more of these RAID lev-
els but typically not all of them. The commonly supported RAID levels are
0, 1, and 5:
RAID 0 (striping and concatenation) does not provide data redundancy,
but striping does improve read/write performance because data is evenly
distributed across multiple disks and typically has the best performance.
Concatenation works best in environments that require small random I/O.
Striping performs well in large sequential or random I/O environments.
➤
RAID 1 (mirroring) provides data redundancy and typically improves
read performance, but writes are typically slower.
➤
RAID 5 is typically slower for both reads and writes when compared to
RAID 1, but the cost is lower. Because multiple I/O operations are
required to compute and store the parity, RAID 5 is slower on write
operation than striping (RAID 0).
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UFS File System Logging
With UFS file system logging, updates to a UFS file system are recorded in
a log before they are applied. In the case of system failure, the system can be
restarted, and the UFS file system can quickly use the log instead of having
to use the
fsck
command.
The
fsck
command is a time-consuming and not always 100% accurate
method of recovering a file system. It reads and verifies the information that
defines the file system. If the system crashed during an update, the update
might have been only partially completed. The
fsck
command must correct
the information by removing these partial updates.
With UFS file system logging, only logged updates are actually applied to
the file system. If the system crashes, the log has a record of what should be
complete and can be used to quickly make the file system consistent.
Solaris Volume Manager (SVM)
The Solaris Volume Manager (previously known as the Solstice DiskSuite) is
a software product that can be used to increase storage capacity and data
availability and in some cases increase performance.
SVM supports four types of related storage components. These are volumes,
state databases (along with replicas), hot spare pools, and disk sets. Table 14.2
