Dell PowerVault 221S Optimizing Dell SCSI Solutions - Page 30

A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS VER A02 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. PAGE 30 11/17/2005