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Appendix A
White Paper: Network Storage LINKSYS © 2007
27 EDCS-593805 v1.0
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Appendix A
Table 1 – Pros and Cons of Different RAID Types
RAID Type Min
Disks
Disk
Tax
Pros Cons
RAID 0 -
(Striped Set)
2 0% Ideal For Higher Performance Read
or Write. No Disk “Tax”. Can Use
100% Of Storage Capacity
No fault tolerance. If one drive fails,
the entire array becomes
inaccessible.
RAID 1 -
(Mirror)
2 50% 100% redundancy data protection.
Can survive a single disk failure.
Single Disk Performance Read or
Write.
High Disk “Tax”, 50% of storage
capacity is dedicated to protection.
RAID 1 +
Spare – (Mirror
+ Spare)
3 66% 100% redundancy and addition
fault-tolerance. Can Survive 2 Disk
Failures. Single Disk Performance
Read or Write.
Very High Disk “Tax”, 66% of total
storage capacity is dedicated to
protection. The spare disk is not
used until a working disk fails.
RAID 5 –
(Striped +
Parity)
3 25% Combination of storage capacity
and performance, with a high
degree (75%) of space usage and
some measure of fault-tolerance.
Higher read performance than
RAID1; similar to RAID 0.
Medium Disk “Tax”, 25% of storage
capacity is dedicated to protection.
Because of the parity that must be
calculated, write transactions are
somewhat slower than read
transactions. It is resource-intensive
to rebuild in the event of a disk
failure (as compared with RAID 1).
RAID 5 +
Spare – (Parity
+ Spare)
4 50% Combination of storage capacity
and performance, with increased
overall system reliability so that
when a disk fails within the array,
the spare can be used to rebuild the
data existing on the failed disk.
Sparing helps to minimize the time
before a disk rebuild is required, so
it minimizes the time that the
system is vulnerable to additional
drive failure
High Disk “Tax”, 50% of storage
capacity is dedicated to protection,
with a minimum of 4 disks.
Because of the parity that must be
calculated, write transactions are
somewhat slower than read
transactions
RAID 10 -
(Mirror Then
Stripe)
4 50% Faster Write Performance Than
RAID 5 (No Parity Calc). Faster
Rebuild Time. This level provides a
high degree of redundancy and can
be used for latency sensitive
applications with high loads due to
its faster write speeds than those
levels that use parity for
calculations. It also increases the
overall system reliability so that
when a drive within the array fails,
the spare can be used to rebuild the
data existing on the failed drive.
High Disk “Tax”, 50% of storage
capacity is dedicated to protection,
with a minimum of 4 disks
JBOD –
(Linear) - (Just
a Bunch of
Disks)
n/a n/a Disks of varied sizes can form a
single logical unit. Unlike RAID 0, if
a single drive fails in a JBOD, only
the data on the affected drive is lost.
In a RAID 0, this usually means the
loss of all the data in the array.
There are no performance benefits
and there is no data protection.