Acer SmartRAID V Uživatelský manuál stáhnout pdf (Strana 184)

7-16

Theory of Operation

RAID 3, as with RAID 2, sector-stripes data across groups of drives, but

one drive in the group is dedicated to storing parity information. RAID 3

relies on the embedded ECC in each sector for error detection. In the case

of drive failure, data recovery is accomplished by calculating the exclusive

OR (XOR) of the information recorded on the remaining drives. Records

typically span all drives, which optimizes the disk transfer rate. Because

each I/O request accesses every drive in the array, RAID 3 arrays can

satisfy only one I/O request at a time. RAID 3 delivers the best

performance for single-user, single-tasking environments with long

records. Synchronized-spindle drives are required for RAID 3 arrays in

order to avoid performance degradation with short records. Because

RAID 5 arrays with small stripes can yield similar performance to RAID 3

arrays, RAID 3 is not supported by SmartRAID V.

RAID 3

Parallel Array with Parity

Read and write operations span all drives.

Parallel access decreases data transfer time

for long sequential records.

DATA DATA DATA DATA DATA

PARITY

RAID 4 is identical to RAID 3 except that large stripes are used, so that

records can be read from any individual drive in the array (except the

parity drive). This allows read operations to be overlapped. However, since

all write operations must update the parity drive, they cannot be

overlapped. This architecture offers no significant advantages over other

RAID levels and is not supported by SmartRAID V.

RAID 4

Parallel Array with Parity

Every write must update dedicated parity drive.

Reads can occur simultaneously

on every data drive.

DATA DATA

PARITY

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Acer SmartRAID V Uživatelský manuál Strana 184