EMC CX500I Configuration Guide - Page 44

Performance

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RAID Types and Trade-offs Table 2-1 Performance, Availability, and Cost of RAID Types (Individual Unit = 1.0) Disk Configuration Relative Read Performance Without Cache Relative Write Performance Without Cache Relative Cost Per Gbyte RAID 5 Group with five Up to 5x with five disks disk s (for small I/O requests that are 2 to 8 Kbytes) Up to 1.25x with five disks 1.25 (for small I/O requests that are 2 to 8 Kbytes) RAID 3 Group with five Up to 4x (for large I/O Up to 4x (for large I/O 1.25 disks requests) requests) RAID 1 mirrored pair Up to 2x Up to 1x 2 RAID 1/0 Group with Up to 10x Up to 5x 2 10 disks Individual unit 1x 1x 1 Notes: These performance numbers are not based on storage-system caching. With caching, the performance numbers for RAID 5 writes improve significantly. Performance multipliers vary with the load on the server and storage system. Performance RAID 5, with individual access, provides high read throughput by allowing simultaneous reads from each disk in the group. RAID 5 write performance is excellent when the storage system uses write caching. RAID 3, with parallel access, provides high throughput for sequential, large block-size requests (blocks of more than 64 Kbytes). With RAID 3, the system accesses all disks in each request but need not read data and parity before writing - advantageous for large requests but not for small ones. RAID 3 uses SP memory without caching, which means you do not need the second SP and SPS that caching requires. Generally, the performance of a RAID 3 Group increases as the size of the I/O request increases. Read performance increases rapidly with read requests up to 1 Mbyte. Write performance increases greatly for sequential write requests that are greater than 256 Kbytes. For applications issuing very large I/O requests, a RAID 3 LUN provides significantly better write performance than a RAID 5 LUN. We do not recommend using RAID 3 in the same storage-system chassis with RAID 5 or RAID 1/0. 2-14 EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide

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2-14
EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide
RAID Types and Trade-offs
Table 2-1
Performance, Availability, and Cost of RAID Types (Individual Unit = 1.0)
Performance
RAID 5, with individual access, provides high read throughput by
allowing simultaneous reads from each disk in the group. RAID 5
write performance is excellent when the storage system uses write
caching.
RAID 3, with parallel access, provides high throughput for
sequential, large block-size requests (blocks of more than 64 Kbytes).
With RAID 3, the system accesses all disks in each request but need
not read data and parity before writing – advantageous for large
requests but not for small ones. RAID 3 uses SP memory without
caching, which means you do not need the second SP and SPS that
caching requires.
Generally, the performance of a RAID 3 Group increases as the size of
the I/O request increases. Read performance increases rapidly with
read requests up to 1 Mbyte. Write performance increases greatly for
sequential write requests that are greater than 256 Kbytes. For
applications issuing very large I/O requests, a RAID 3 LUN provides
significantly better write performance than a RAID 5 LUN.
We do not recommend using RAID 3 in the same storage-system
chassis with RAID 5 or RAID 1/0.
Disk Configuration
Relative Read
Performance
Without Cache
Relative Write
Performance
Without Cache
Relative
Cost Per
Gbyte
RAID 5 Group with five
disks
Up to 5x with five disks
(for small I/O requests
that are 2 to 8 Kbytes)
Up to 1.25x with five disks
(for small I/O requests that
are 2 to 8 Kbytes)
1.25
RAID 3 Group with five
disks
Up to 4x (for large I/O
requests)
Up to 4x (for large I/O
requests)
1.25
RAID 1 mirrored pair
Up to 2x
Up to 1x
2
RAID 1/0 Group with
10 disks
Up to 10x
Up to 5x
2
Individual unit
1x
1x
1
Notes: These performance numbers are not based on storage-system caching. With caching,
the performance numbers for RAID 5 writes improve significantly.
Performance multipliers vary with the load on the server and storage system.