Apple Xserve RAID User's guide User's Guide download pdf (Page 61)

RAID Overview 61

RAID 3: Parallel transfer with parity on dedicated disk

RAID level 3 adds redundant information to a striped set of drives with parallel access,

allowing regeneration and reconstruction in the event of a disk failure. The parity data is

stored on one disk dedicated to this purpose. RAID 3 provides high transfer rates and high

reliability and availability, at a lower cost than RAID levels that incorporate mirroring.

RAID 3 requires a minimum of three drives.

RAID 5: Independent data disks with distributed parity

By distributing the parity information across all drives in a set, RAID level 5 alleviates the

write bottleneck intrinsic to RAID 3, and achieves high reliability and data availability.

However, RAID 5 can result in asymmetrical performance—better read than write. For this

reason, RAID 5 is often augmented with related storage technologies such as caching.

RAID 5 offers the highest read data transaction rate of all levels along with a medium write

rate. The low ratio of ECC parity disks to data disks offers hardware efﬁciency. Disk failure

has a moderate impact on the total transfer rate, and this level also incorporates the most

complex controller design.

RAID 5 requires a minimum of three drives.

Preconfigured Level 5 on the Xserve RAID System

The Xserve RAID system is preconﬁgured with RAID 5. The speed and capacity of the

system’s hardware and RAID controllers make this level an optimum conﬁguration for most

storage needs. Apple recommends that you use this preconﬁgured RAID 5 setup.

Hardware and Software RAID

In addition to the RAID levels described above, which you create with the RAID Admin

application on the CD that came with your system, you can use Apple RAID (part of Disk

Utility in Mac OS X) to augment level 1, 3, or 5. These software-conﬁgured variations are

known as RAID 10, 30, and 50.

RAID 10

RAID level 10 uses software to stripe data across the two controllers for redundancy or

enhanced performance.

To create a RAID 10 conﬁguration, you use RAID Admin ﬁrst and Disk Utility second. See the

document “Using RAID Admin and Disk Utility” on the CD that came with your system for

instructions. After you’ve used Disk Utility to set RAID 10, this conﬁguration appears as one

disk on the host system.

1 2 ... 56 57 58 59 60 61 62 63 64 65 66 ... 91 92

No comments

Apple Xserve RAID User's guide User's Guide Page 61