IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 2. Hardware configuration planning 39

failure by having a mirror copy of each disk. By combining the two, RAID 10 provides data

protection and good I/O performance.

2.8.4 Combination of RAID 5 and RAID 10 arrays

It is possible to have RAID 10 and RAID 5 arrays configured within the same loop or

enclosure, as illustrated in Figure 2-19.

Figure 2-19 RAID 5 and RAID 10 in the same loop

2.8.5 RAID 5 versus RAID 10 performance

You may be asking which is better, RAID 5 or RAID 10? As with most complex issues, the

answer is that it depends. There are a number of workload attributes that influence the

relative performance of RAID 5 versus RAID 10, including the use of cache, the relative mix of

read versus write operations, and whether data is referenced randomly or sequentially.

Random and sequential reads and random writes

When a storage server receives a read request from a host, the storage server first looks to

see if the requested data is in cache. If it is, there is no need to read the data from disk, and

so it does not matter whether RAID 5 or RAID 10 is used.

For reads which must be satisfied from disk, performance of RAID 5 and RAID 10 are roughly

equal, except at high I/O rates. If RAID 5 contains significantly more data than RAID 10 array,

data are located on the inside tracks of disks that it takes longer seek time that sometimes

RAID 5 become slower than RAID 10. But if RAID 5 contains almost same amount of data,

Note: If you make a RAID 5 array first and then make RAID 10 in the first or second

enclosure, three hot spare disks are made and it will reduce the total effective capacity. To

avoid this, you should create the RAID 10 Array in the first or second enclosure.

IBM

TotalStorage

RAID 5+10 configuration example

 When using same capacity and rpm.

data spare

mirror

1

st

RAID10:3+3+2S

DA

DA

1750-511

1750-EX1-1

1750-EX1-3

1750-EX1-2

Loop 0

Loop 1

parity (float)

1

st

RAID5:6+P+S

2

nd

RAID10:3+3+2S

If first array is RAID 5 and second array is RAD10 in

first two enclosures, three hot spares are made.

2

nd

RAID5:7+P