Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS, Руководство администратора

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54 SLES 10 Storage Administration Guide for EVMS
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6.1.2 Overview of RAID Levels
The following table describes the advantages and disadvantages of the RAID levels supported by
EVMS. The description assumes that the component devices reside on different disks and that each
disk has its own dedicated I/O capability.
IMPORTANT: For information about creating complex or nested RAID devices with mdadm, see
Chapter 7, “Managing Software RAIDs 6 and 10 with mdadm,” on page 75 .
Table 6-2
RAID Levels Supported by EVMS
RAID processing In the host server’s processor RAID controller on the disk array
RAID levels 0, 1, 4, 5, and 10 plus the
mdadm
raid10
Varies by vendor
Component devices Disks from same or different disk
array Same disk array
RAID Level Description Performance and Fault Tolerance
0 Stripes data using a round-
robin method to distribute
data over the RAID’s
component devices. Improves disk I/O performance for both reads and writes.
Actual performance depends on the stripe size, the actual
data, and the application.
Does not provide disk fault tolerance and data redundancy.
Any disk failure causes all data in the RAID to be lost.
1 Mirrors data by copying
blocks of one disk to another
and keeping them in
continuous synchronization.
If disks are different sizes,
the smaller disk determines
the size of the RAID. Improves disk reads by making multiple copies of data
available via different I/O paths. The write performance is
about the same as for a single disk because a copy of the
data must be written to each of the disks in the mirror.
Provides 100% data redundancy. If one disk fails then the
data remains available on its mirror, and processing
continues.
4 Stripes data and distributes
parity in a round-robin
fashion across all disks. If
disks are different sizes, the
smaller 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.
Feature Linux Software RAID Hardware RAID