On Sat, 2003-11-01 at 10:27, David Krider wrote:
On Sat, 2003-11-01 at 09:16, H du Plooy wrote:
It's been mentioned several times on this list that 3ware makes the only linux supported *hardware* IDE raid cards.
So if a card is not a hardware card, as I understand it, you need the driver to do the actual work. If you need the driver for that, how do you boot off it (i.e. access the raid volume before the kernel with neccessary drivers are loaded)? Or aren't the software based ones bootable?
Hardware cards setup their config in the BIOS, before the OS ever gets booted. From there, you can setup "virtual" drives that, say, the SuSE installer will see as /dev/hda, /dev/hdb, etc. The OS won't know the difference. I'm going to order a machine to do this today, using a 3ware card.
Software arrays don't rely on a card. There's no such thing as a software RAID card. Software arrays are setup AFTER the OS is booted. I have an old HP machine here that doesn't have a RAID card in it. It simply has a dual-channel SCSI controller. I installed SuSE onto the first drive, made the second my swap partition, then setup a software raid over the other 4 and mounted it on /data. This is all done through ``md''.
If you can afford it, always go with hardware RAID first. It doesn't cost the OS anything to run on hardware RAID. Software RAID requires the OS to do the work of keeping the array in sync.
Regards, dk
You correctly describe hardware raid cards like 3ware and software MD, but I think the question was about hybrid cards like at least some of the Promise cards. I have not used Promise, but from what I understand, the "driver" is basically part of the card. So when a disk write is performed, the hardware somehow causes the CPU to execute extra instructions which it provides to the CPU. These extra instructions do all the RAID implementation. As you can tell, I'm out of my league. I will say I have used the 3ware and find them great. Specifically, I use 3ware as boot disks under both Linux and Win2K. Greg -- Greg Freemyer