Overland Storage SnapServer Administrator's Manual page 262

SnapServer 7.0 Administrator's Guide
capacities are very large, it may take many hours to rebuild the pool. If a second disk fails
before the rebuild has completed, all the data in the pool will be lost. That is to say, large
capacity disks increase the time taken to rebuild the pool, during which time the pool is
vulnerable to a second disk failure. Moreover, the chance of a second disk failure increases
as the number of disks in the pool increases.
RAID 5 is similar to RAID 0 in that data is striped across multiple disks. However, one
disks worth of space is reserved to store parity data, which can be used to reconstruct the
pool in the event of one of its disks failing. With RAID 5, the parity data is distributed
across all the disks in the pool. If a single disk fails, each block of data stored on that disk
can be reconstructed using the corresponding data block from all the other disks along with
the parity block. This means that if a single disk fails, data can still be read, albeit at a
rather slower rate (because it needs to be reconstructed, rather than read directly). For this
reason, a RAID 5 pool with a disk failure is referred to as a degraded pool.
RAID 6 (Striping with Dual Parity)
RAID 6 is similar to RAID 5 but instead of storing a single disk's worth of parity data, two
disk's worth are stored, making the pool capable of withstanding the failure of two disks.
However, there is an additional write overhead involved in calculating the double parity
data. Since RAID 6 works best with dedicated hardware, RAID 6 is only offered on systems
with a hardware RAID controller. Read performance is similar to that of RAID 0 or 5. Since
two disks are used for storing parity data, the capacity of a RAID 6 pool made up of 8 x 500
GB disks will be 3 TB.
RAID 10 (Striped Mirroring)
RAID 10 is defined as mirrored stripe sets or also known as RAID 0+1. You can build RAID
10 either directly through the RAID controller (depending on the controller) or by
combining software mirroring and controller striping, or vice versa (called RAID 01).
RAID 50
A RAID 50 combines the straight block-level striping of RAID 0 with the distributed single
parity of RAID 5. That is, a RAID 0 array striped across RAID 5 elements. It requires at
least 6 disks. This can increase the performance by allowing the controller to more
efficiently cluster commands together. Fault tolerance is also increased, as one drive can
fail in each individual array.
RAID 60
A RAID 60 combines the straight block-level striping of RAID 0 with the distributed double
parity of RAID 6. That is, a RAID 0 array striped across RAID 6 elements. It requires at
least 8 disks. This can increase the performance by allowing the controller to more
efficiently cluster commands together. Fault tolerance is also increased, as two drives can
fail in each individual array.
Recurring Snapshot
A snapshot that runs at an administrator-specified time and interval.
Restrict Anonymous
A Windows feature in which anonymous users cannot list domain user names and
enumerate share names. Microsoft has provided a mechanism in the Registry called restrict
anonymous for administrators to restrict the ability for anonymous logon users (also known
as NULL session connections) to list account names and enumerate share names.
The implementation of the restrict anonymous mechanism may prevent the SnapServer
from obtaining the list of account names it needs to authenticate Windows domain users.
10400317-001 10/2011
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