Guidelines For Component Devices - Novell LINUX ENTERPRISE SERVER 10 SP2 - STORAGE ADMINISTRATION GUIDE 05-15-2009 Administration Manual

6.1.7 Guidelines for Component Devices

For efficient use of space and performance, the disks you use to create the RAID should have the
same storage capacity. Typically, if component devices are not of identical storage capacity, then
each member of the RAID uses only an amount of space equal to the capacity of the smallest
member disk.
Version 2.3 and later of
mdadm
support component devices up to 2 TB in size.
IMPORTANT: If you have a local disk, external disk arrays, or SAN devices that are larger than the
supported device size, use a third-party disk partitioner to carve the devices into smaller logical
devices.
You can combine up to 28 component devices to create the RAID array. The
create can be up to the maximum device size supported by the file system you plan to use. For
information about file system limits for SUSE
Support" in the SUSE Linux Enterprise Server 10 Installation and Administration Guide. (http://
www.novell.com/documentation/sles10).
In general, each storage object included in the RAID should be from a different physical disk to
maximize I/O performance and to achieve disk fault tolerance where supported by the RAID level
you use. In addition, they should be of the same type (disks, segments, or regions).
Using component devices of differing speeds might introduce a bottleneck during periods of
demanding I/O. The best performance can be achieved by using the same brand and models of disks
and controllers in your hardware solution. If they are different, you should try to match disks and
controllers with similar technologies, performance, and capacity. Use a low number of drives on
each controller to maximize throughput.
IMPORTANT: As with any hardware solution, using the same brand and model introduces the risk
of concurrent failures over the life of the product, so plan maintenance accordingly.
The following table provides recommendations for the minimum and maximum number of storage
objects to use when creating a software RAID:
Recommended Number of Storage Objects to Use in the Software RAID
Table 6-6
RAID Type
RAID 0 (striping)
RAID 1 (mirroring)
RAID 4 (striping with dedicated parity)
RAID 5 (striping with distributed parity)
Connection fault tolerance can be achieved by having multiple connection paths to each storage
object in the RAID. For more information about configuring multipath I/O support before
configuring a software RAID, see
supports component devices up to 4 TB in size each. Earlier versions
®
Linux Enterprise Server 10, see "Large File System
Minimum Number of
Storage Objects
2
2
3
3
Chapter 5, "Managing Multipath I/O for Devices," on page
RAID device you
md
Recommended
Maximum Number of
Storage Objects
8
4
8
8
Managing Software RAIDs with EVMS
43.
79