Dell PowerVault 221S (SCSI) - Manual (Page 35)

A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS VER A02
PAGE 35 11/17/2005
• Table 5-1: Pros and Cons for Spanning Arrays with various RAID Levels
Note: Dell PERC controllers don’t support spanning of arrays across different
controllers. Spanning across channels on the same PERC controller is only
supported.
Capacity Needs – Virtual Disk Size
Virtual disks on SCSI PERC controllers cannot be created with an aggregate
size greater than 2TB due to limitations on SCSI controllers and operating
systems. Host management application (OMSM, Array Manager) will give an
error if an attempt is made to make virtual disk greater than 2TB, prompting
user to reduce size of virtual disk. For more information please refer to
“Beyond The 2-TB SCSI Logical Unit” white paper at:
http://www.dell.com/downloads/global/vectors/2004_2tblun.pdf .
Additional RAID information
o Dell ‘Getting Started with RAID’ document
http://support.dell.com/support/edocs/storage/RAID/RAIDbk0.pdf
Level Pros Cons
RAID 0
Improves data throughput by
optimizing bandwidth utilization
Reduces reliability and availability of data
with additional point of failure – second
channel
RAID 1
Improves data availability
against channel failures, if
mirrored set is spanned across
separate channel
If PV22xS is used on both channels
(either in Split of Joined topology), limits
the usage of PERC on internal channel
(connecting devices to the same channel
on internal and external connectors is
not supported)
RAID 5
May improve data throughput for
certain accesses, if data and
parity for the access span
across channels Even though RAID5 provides data
protection but compromises reliability
and availability of data at SCSI channel
level
RAID 10
Improves data availability
against channel failures, if
mirrored set is spanned across
separate channel
If PV22xS is used on both channels
(either in Split of Joined topology), limits
the usage of PERC on internal channel
(connecting devices to the same channel
on internal and external connectors is
not supported)
RAID 50
May improve data throughput,
similar to spanned RAID5
Reduces reliability and availability of data
as compared to non-spanned RAID50 at
SCSI channel level