Dell Compellent Series 30 - Manual (Page 441)

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Port
The physical connection point on servers, switches, Storage Center controller, and disk drive enclosures
that is used to connect to other devices in the system. Ports on a FC network are identified by their
Worldwide Port Name (WWPN); on iSCSI networks, ports are given an iSCSI name.
Preallocation
Pre-allocating storage physically assigns storage to the volume before its use by the server. Not allowed for
volumes already having Replays.
Q
QoS Definition
Quality of Service. A networking term that specifies a guaranteed throughput level to guarantee end-to end
latency will not exceed a specified level.
R
RAID (Redundant Array of Independent Disks)
A way of encoding data over multiple physical disks to ensure that if a hard disk fails a redundant copy of
the data can be accessed instead. Example schemes include mirroring and RAID-5.
RAID 0
Stripes data but provides no redundancy. If one disk fails, all data is lost. Do not use RAID 0 unless data is
back-up elsewhere.
RAID 5-5 and 5-9
Maintains a logical copy of the data using a mathematically derived rotating parity stripe across 5 or 9 disks.
The parity stripe is derived from the data stripes. This method has less overhead for the redundant
information than RAID 10; however write performance is slower than RAID 10 due to the calculation of the
parity stripe for every write.RAID 5 protects against data loss when any single disk fails. RAID 5-5 is 80%
efficient. RAID 5-9 is 89% efficient.
RAID 6-6 and 6-10
RAID 6 protects against data loss when any 2 disks fail. RAID 6-6 is 67% efficient. RAID 6-10 is 80%
efficient.
RAID 10
Striped and mirrored. Provides both data availability and top performance. Maintains a minimum of one full
copy of all data on the volume. RAID 10 provides optimum Read / Write performance, increased probability
of withstanding multiple failures, and the fastest restoration of data.
RAID 10-DM
RAID 10 Dual Mirror provides maximum protection for storage. Data is written simultaneously to three
separate disks. All three disks return a write acknowledgement. RAID 10 protects against data loss when
any 2 disks fail.