System And Performance Expectations; Raid Levels - HP 4400 Enterprise Installation Manual

System and performance expectations

To help determine the best way to configure your storage, rank the following three storage
characteristics in order of importance:
Fault tolerance (high availability)
I/O performance
Storage efficiency
With your priorities established, you can determine which striping method and RAID level to use.
As highlighted in the following section, some configuration methods offer greater fault tolerance,
while other configuration methods offer better I/O performance or storage efficiency.

RAID levels

Vraid is the HP term for the implementation of RAID (Redundant Array of Independent Disks) storage.
Vraid is also referred to as redundancy in HP management software. Virtual disks with HP Vraid
use three key RAID methods: data striping, data mirroring, and parity error checking. Unlike
traditional RAID, all HP Vraid levels distribute data across all available physical disks.
Data striping improves speed by performing virtual disk I/O with an entire group of physical disks
at the same time. Mirroring provides data redundancy by storing data and a copy of the data.
Parity also provides data redundancy by storing data and the calculated parity for each stripe of
data. If a subset of the data on a physical disk becomes corrupt or the entire physical disk fails,
the data can be automatically recovered from redundancy so that data loss does not occur.
The EVA has four Vraid types: Vraid0, Vraid1, Vraid5, and Vraid6. Each Vraid type provides
unique I/O speed and has a different level of data redundancy, which directly effects the amount
of physical space used. Once a virtual disk is created, the Vraid type or level cannot be changed.
See Table 1 (page 6)
Table 1 Raid Level Comparison
Summary
Vraid0 Vraid0 is optimized for I/O
speed and efficient use of
physical disk capacity, but
provides no data redundancy. required. Consider Vraid0 only for
Vraid1 Vraid1 is optimized for data
redundancy and I/O speed,
but uses the most physical disk
space.
IMPORTANT: Vraid1 uses
about 100% more physical
disk space than Vraid0.
Vraid5 Vraid5 provides a balance of
data redundancy, I/O speed,
and efficient use of physical
disk space. Vraid5 uses about
20% more physical disk space
than Vraid0.
Vraid6 Vraid6 is similar to Vraid5, but
provides a higher level of
redundancy by storing two
parity blocks per stripe instead
6 Review and confirm your plans
for a comparison of the different RAID levels.
Best practices
IMPORTANT: HP does not
recommend using Vraid0 for virtual
disks when high availability is
noncritical storage. Vraid0 virtual
disks provide the best performance
for applications that use random I/O.
In general, Vraid1 virtual disks
provide better performance
characteristics over a wider range of
application workloads than Vraid5.
Vraid5 virtual disks provide as good
or better performance than Vraid1
for applications that use sequential
writes. Vraid5 has much lower
random write performance in
comparison to Vraid1, but has much
higher capacity efficiency.
Performance characteristics of Vraid6
for random and sequential write
workloads will be slightly slower than
Vraid5. Vraid6 provides the highest
Data redundancy RAID method
None Striping
High Striping and
mirroring
Medium Striping and
parity
Very high Striping and
double parity