On Thu, Dec 01, 2005 at 05:44:12PM +0000, Christoph Hellwig wrote: > On Thu, Dec 01, 2005 at 08:44:15AM -0500, Salyzyn, Mark wrote: > > The HostRAID driver has a specialized (ok, yes, also proprietary) CHIM > > and sequencer where attention can be focused on techniques of > > performance improvement and OS agnostics. In addition, the RAID code in > > that driver understands the hardware, CHIM & sequencer and takes > > advantage of features that just can not be performed by an abstracted dm > > or an LLD. RAID1 is handled under some conditions, for instance, with > > one DMA operation over the PCI bus rather than two duplicated for each > > target, greatly increasing the performance. > > If you contributed that sequencer code and sent me a card I'm pretty sure > I'd love into adding support for this to a special DM module. In fact we'd > need somthing similar for Certain SATA boards aswell. > > OTOH the raid flag would be useless aswell there, because we'd of course > support this on identical cards without the raid bios aswell :) I'd love to see a hardware-aware DM RAID module, since I want to do the same thing for sata_sx4 (Promise SX4). SX4 has four ATA engines, an on-card ECC-capable DIMM, and an on-card XOR engine. The OS driver has complete control over these facilities. Unfortunately, driving the card in "dumb mode" means that performance takes a major hit, since each transaction looks like: submit DMA memcpy to HDMA engine get HDMA interrupt # now, the data is on the card submit ATA write command get ATA interrupt All data must be copied to/from the DIMM, before the ATA engine can do anything. Further, there is only one HDMA engine, but 4 ATA engines. Ideally, RAID1 would copy the data to the card ONCE, then start 2 ATA engines. Ideally, RAID5 would copy the data to the card ONCE, XOR it, then start the ATA engines. And the rest of the DIMM should be used as write-through cache. I'm sure DM can do that, but I haven't researched how. I'll supply a card (and engineering help, but no docs, alas) to anyone interested in trying out this stuff. Jeff - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
