Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007, Руководство администратора

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Managing Software RAIDs with EVMS 61
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6.1.3 Comparison of RAID Performance
The following table compares the read and write performance for RAID devices.
Table 6-3
Read and Write Performance for RAIDs
6.1.4 Comparison of Disk Fault Tolerance
The following table compares the disk fault tolerance for RAID devices.
Table 6-4
Fault Tolerance for RAIDs
5 Stripes data and distributes
parity in a round-robin
fashion across all disks. If
disks are different sizes, the
smallest disk determines the
size of the RAID. Improves disk I/O performance for reads and writes. Write
performance is considerably less than for RAID 0, because
parity must be calculated and written. Write performance is
faster than RAID 4. Read performance is slower than for a
RAID 1 array with the same number of component disks.
Actual performance depends on the number of component
disks, the stripe size, the actual data, and the application.
Provides disk fault tolerance. If a disk fails, performance is
degraded while the RAID uses the parity to reconstruct data
for the replacement disk. Provides slightly less data
redundancy than mirroring because it uses parity to
reconstruct the data.
Raid Level Read Performance Write Performance
0 Faster than for a single disk Faster than for a single disk and other
RAIDs.
1 Faster than for a single disk, increasing as
more mirrors are added Slower than for a single disk, declining as
more mirrors are added.
4 Faster than for a single disk. Slower than a
RAID 0 because one disk is used for parity. Faster than for a single disk. Slower than a
RAID 0 because of writes for parity. Slower
than a RAID 5 because of possible
bottlenecks for writes of parity to the
dedicated parity disk.
5 Faster than for a single disk; comparable to a
RAID 0. Faster than a single disk. Slower than a
RAID 0 because of writes for parity.
Raid Level Number of Disk Failures Tolerated Data Redundancy
0 None No
1 Number of disks minus 1 100% redundancy for each mirror
4 1 Dedicated parity disk to reconstruct data. If
the parity disk fails, all parity must be
recalculated.
RAID Level Description Performance and Fault Tolerance