HP Surestore Disk Array 12h and FC60 - Manual (Page 49)

Disk Array High Availability Features 49
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Figure 17 Calculating Data Parity
Data Striping
Data striping, which is used on RAID 0, 0/1, 3 and 5 LUNs, is the performance-enhancing
technique of reading and writing data to uniformly sized segments on all disks in a LUN
simultaneously. Collectively, the segments comprise a stripe of data on the LUN. Data
striping enhances performance by allowing multiple sets of read/write heads to execute the
same I/O transaction simultaneously.
The amount of information simultaneously read from or written to each disk is the stripe
segment size. The stripe segment size is configurable to provide optimum performance
under varying sizes of I/O transactions. Stripe segment size is specified in 512-byte blocks
of data.
Stripe segment size can affect disk array performance. The smaller the stripe segment size,
the more efficient the distribution of data read or written across the stripes in the LUN.
However, if the stripe segment is too small for a single I/O operation, the operation requires
access to two stripes. Called a stripe boundary crossing, this action may negatively impact
performance.
The optimum stripe segment size is the smallest size that will rarely force I/Os to a second
stripe. For example, assume your application uses a typical I/O size of 64
K
B. If you are
1
0
0
1
0
0
0
1
1
1
0
1
0
1
1
1
0
1
0
1
0
1
0
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1
0
0
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0
0 = + + + +
Data Data Data Data Parity
If this bit is
now written
as 1...
This bit will also
be changed to a 1
so the total still
equals 0.