Avago Technologies MegaRAID SATA 150-4 (523) - Manual (Page 42)

2-20 Introduction to RAID
Copyright © 2003–2006 by LSI Logic Corporation. All rights reserved.
A hot swap is the manual substitution of a replacement unit in a disk
subsystem for a defective one, where the substitution can be performed
while the subsystem is running hot swap drives. Auto-Rebuild in the
BIOS Configuration Utility allows a failed drive to be replaced and
automatically rebuilt by hot-swapping the drive in the same drive bay. The
RAID array continues to handle requests while the rebuild occurs,
providing a high degree of fault tolerance and zero downtime.
Table 2.10
describes the fault tolerance features of each RAID level.
Table 2.10 RAID Levels and Fault Tolerance
RAID
Level
Fault Tolerance
0 Does not provide fault tolerance. All data lost if any drive fails. Disk striping writes data across
multiple disk drives instead of just one disk drive. It involves partitioning each drive storage
space into stripes that can vary in size. RAID 0 is ideal for applications that require high
bandwidth but do not require fault tolerance.
1 Provides complete data redundancy. If one disk drive fails, the contents of the other disk drive
can run the system and reconstruct the failed drive. The primary advantage of disk mirroring is
that it provides 100% data redundancy. Since the contents of the disk drive are completely written
to a second drive, no data is lost if one of the drives fails. Both drives contain the same data at
all times. RAID 1 is ideal for any application that requires fault tolerance and minimal capacity.
5 Combines distributed parity with disk striping. Parity provides redundancy for one drive failure
without duplicating the contents of entire disk drives. If a drive fails, the RAID controller uses
the parity data to rebuild all missing information. In RAID 5, this method is applied to entire
drives or stripes across all disk drives in an array. Using distributed parity, RAID 5 offers fault
tolerance with limited overhead.
10 Provides complete data redundancy using striping across spanned RAID 1 arrays. RAID 10
works well for any environment that requires the 100 percent redundancy offered by mirrored
arrays. RAID 10 can sustain a drive failure in each mirrored array and maintain drive integrity.
50 Provides data redundancy using distributed parity across spanned RAID 5 arrays. RAID 50
includes both parity and disk striping across multiple drives. If a drive fails, the RAID controller
uses the parity data to recreate all missing information. RAID 50 can sustain one drive failure
per RAID 5 array and still maintain data integrity.