Hitachi Universal Storage Platform V Reference Manual page 47

RAID-10 using 2D + 2D and 3390-x LDEVs
Track 0
to
Track 7
Track 16
to
Track 23
Track 32
to
Track 39
Track 48
to
Track 55
Figure 3-1 Sample RAID-10 2D + 2D Layout
RAID-5. A RAID-5 array group consists of four (3D+1P) or eight (7D+1P)
data drives. The data is written across the four (or eight) drives in a stripe that
has three (or seven) data chunks and one parity chunk. Each chunk contains
either eight logical tracks (mainframe) or 768 logical blocks (open). The
enhanced RAID-5+ implementation in the USP V/VM minimizes the write
penalty incurred by standard RAID-5 implementations by keeping write data in
cache until an entire stripe can be built and then writing the entire data stripe
to the drives. The 7D+1P RAID-5 increases usable capacity and improves
performance.
Figure 3-2 illustrates RAID-5 data stripes mapped over four physical drives.
Data and parity are striped across each of the data drives in the array group
(hence the term "parity group"). The logical devices (LDEVs) are evenly
dispersed in the array group, so that the performance of each LDEV within the
array group is the same.
"Exclusive OR" (EOR) of the data chunks. The parity and data chunks rotate
after each stripe. The total data in each stripe is either 24 logical tracks (eight
tracks per chunk) for mainframe data, or 2304 blocks (768 blocks per chunk)
for open-systems data. Each of these array groups can be configured as either
3390-x or OPEN-x logical devices. All LDEVs in the array group must be the
same format (3390-x or OPEN-x). For open systems, each LDEV is mapped to
a SCSI address, so that it has a TID and logical unit number (LUN).
Functional and Operational Characteristics
Hitachi Universal Storage Platform V/VM User and Reference Guide
Track 0 Track 8
to to
Track 7 Track 15
Track 16 Track 24
to to
Track 23 Track 31
Track 32 Track 40
to to
Track 39 Track 47
Track 48 Track 56
to to
Track 55 Track 63
Figure 3-2 also shows the parity chunks that are the
Track 8
to
Tra ck 15
Track 24
to
Track 31
Tra ck 40
to
Tra ck 47
Track 56
to
Track 63
3-3