Dell PowerVault 221S (SCSI) - Manual (Page 30)

A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS VER A02
PAGE 30 11/17/2005
Controller Family
Aside from the technical, physical and feature differences between the controller families
(see Table 5-2), there are a few critical differences which impact behavior of these
controllers and hence a storage solution. Dell’s Storage controllers can be broadly
categorized into two families – Adaptec PERCs and LSI PERCs. Design of these families
impact the customer experience and may lead to ambiguities when configuring more
complex storage strategies/solutions.
Though most of these differences are transparent to the user, when using the
recommended Dell OpenManage™ software to configure storage subsystem; however, in
cases where the BIOS utility is the preferred tool, an in-depth understanding of controller
behavior is required to avoid possible issues. These differences include:
• Controller BIOS utility terminology and operation
o The user interfaces of the boot-time BIOS utilities for the different
controller families differ in layout and terminology. In environments where
controllers from both families are being managed via the BIOS utilities,
these differences can lead to confusion. Refer to user guides for
controller specific information on the functionality and terminology used
by these utilities.
NOTE: In the context of this document, the word ‘array’ (LSI BIOS) =
‘container’ (Adaptec BIOS) = ‘logical drive’ (LSI POST) = ‘volume’
(OpenManage Software).
• Layout of multiple logical arrays on the same group of disks
o LSI family of controllers require that once an array is created on a group
of disks, any subsequent arrays created on any of these same disks can
only be created on the same group of disks; subsequent arrays are not
allowed to use any disks not in the original group, nor any subset of the
original group. Adaptec controllers are less restrictive in this regard.
o Similarly LSI controllers are more restrictive of hot spare functionality in
this scenario. If redundant and non-redundant arrays are placed on the
same group of disks and a hot spare is assigned to the redundant array,
because of the non-redundant array’s failed state, the hot spare will
never start the rebuild on the redundant array.
• Mixed-size hard drives within a RAID10/RAID50
o RAID50 not supported on Adaptec controllers. This configuration is
supported on LSI controllers only
o When mixing drive sizes in RAID10/RAID50 on LSI controllers, with
default maximum size, the controller will not coerce the larger ‘child’
arrays to match the size of the smallest ‘child’ array. Controller will stripe
across all ‘child’ arrays until the smallest one is full, then it will continue to
stripe across the remaining ‘child’ arrays until the next one is full, and so
on until all the available space is used. This can impact performance as
the array fills up, since the number of stripes decreases as ‘child’ arrays
fill up.