Arrays
See
Figure 4
. With an array controller installed in the system, the capacity of several physical drives
(P1–P3) can be logically combined into one or more logical units (L1) called arrays. When this is
done, the read/write heads of all the constituent physical drives are active simultaneously, dramatically
reducing the overall time required for data transfer.
NOTE:
Depending on the storage server model, array con
fi
guration may not be possible or necessary.
P1
P3
P2
L1
gl0042
Figure 4 Con
fi
guring arrays from physical drives
Because the read/write heads are simultaneously active, the same amount of data is written to each
drive during any given time interval. Each unit of data is termed a block. The blocks form a set of data
stripes over all the hard drives in an array, as shown in
Figure 5
.
S1
S2
S3
S4
B1
B4
B7
B2
B5
B8
B11
B10
B12
B6
B3
B9
gl0043
Figure 5 RAID 0 (data striping) (S1-S4) of data blocks (B1-B12)
For data in the array to be readable, the data block sequence within each stripe must be the same.
This sequencing process is performed by the array controller, which sends the data blocks to the drive
write heads in the correct order.
A natural consequence of the striping process is that each hard drive in a given array contains the
same number of data blocks.
NOTE:
If one hard drive has a larger capacity than other hard drives in the same array, the extra capacity is
wasted because it cannot be used by the array.
Fault tolerance
Drive failure, although rare, is potentially catastrophic. For example, using simple striping as shown in
Figure 5
, failure of any hard drive leads to failure of all logical drives in the same array, and hence to
data loss.
HP ProLiant Storage Server
31
Summary of Contents for DL320s - ProLiant 9TB SATA Storage Server NAS
Page 14: ...14 About this guide ...
Page 28: ...28 Installing and configuring the server ...
Page 36: ...36 Storage management overview ...
Page 68: ...68 File server management ...
Page 74: ...74 Print services ...
Page 96: ...96 Enterprise storage servers ...
Page 120: ...120 Troubleshooting servicing and maintenance ...
Page 122: ...122 System recovery ...