Raid-1: Mirroring - HP xw4400 Mini White Paper

Figure 1. Efficiency of Software RAID-0
Read Performance
Excellent
Read performance is
excellent, scaling
towards controller
maximum speed as
more disks are added.
The use of multiple
controllers will aid in
scaling.

RAID-1: Mirroring

RAID-1, or mirroring, means that the data is copied or mirrored across multiple physical disks. The
data from a single physical disk or partition, once put into a RAID-1 array, will be copied
transparently to the other disks in the array. This provides increased reliability for data integrity;
should one disk fail, the data still remains on the other(s).
Tip:
Although RAID-1, as well as other RAID levels such as RAID-5, does provide
some data protection, this is only protection against common hardware
problems such as failure of a single disk. RAID should not be viewed as a
substitute for regular data back-ups.
Since it is possible to read from two (or more) disks at once, there is a possible performance increase
using RAID-1. Typically performance is sacrificed for recovery of data. Because data is mirrored, only
half of the physical space is utilized, and data must be replicated to multiple disks, marginally
increasing write times. Software RAID-1 is supported by HP Linux workstations.
Figure 2. Efficiency of Software RAID-1
Read Performance
Slight Improvement
Theoretically, RAID-1
configuration could
deliver higher read
performance, but there
have not been
significant gains seen
using software RAID-1.
Write Performance
Excellent
Write performance is
excellent as well,
typically scaling even
better than reads.
Write Performance
Somewhat Slower
Writes will be
fractionally slower than
non-RAID configurations
since data must be
replicated to several
disks.
Space Efficiency
~100%
Space efficiency is quite
good; there is very little
overhead.
Space Efficiency
~50%
Only 50% space
efficiency for two-disk
RAID-1, since the data
is fully replicated on
each disk.
Reliability
Decreased
RAID-0 offers no
protection against disk
crashes; in fact, it is
somewhat worse than
non-RAID configurations
because a single disk
crash is guaranteed to
affect the data spread
out over the array.
Reliability
Excellent
Reliability is very good;
if one disk crashes, the
other(s) still have a full
copy of the data.
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