On 5/3/2011 11:05 AM, Paul Anderson wrote:
I'm still perfectly willing to buy good HW RAID cards, don't get me
wrong, but their main benefit to me will be the battery backed cache,
not the performance.
Good RAID cards have many more advantages than battery cache and
performance. One is moving a RAID card and its attached arrays from a
failed host to a new one. In the case of the hardware RAID card usually
all that is required is loading the HBA driver and mounting the
filesystem. Such a move of an mdraid array is usually, well, not nearly
as straightforward, to put it kindly.
Keep in mind that it is hard to balance a HW RAID card across multiple
SAS expanders -you can certainly get a -16e card of some sort, but
then it does ALL of the I/O to those 4 expanders ALL of the time.
I'm note sure I know exactly what you mean here Paul. You seem to be
talking about RAID card <-> drive chassis cabling flexibility and
symmetrical bandwidth. The following two SAS expander/switch products
are likely worth a quick read:
Using an LSI 9260-4i single 8087 port RAID card, the Intel expander, and
some 8087/8088 panel converters, one could attach *5* x 24 drive LSI
620J SAS JBOD chassis for a total of 120 drives with equal bandwidth
to/from all drives, about 2GB/s total bandwidth, RAID ASIC limited. Few
would want to connect 120 drives to such a single port RAID controller,
but this example demonstrates that symmetry can be achieved across a
large number of cascaded SAS expander ASICs (6 total) with a lot of drives.