On Sun, Aug 26, 2007 at 02:01:24AM -0400, Lennart Sorensen wrote: > Linux software raid (at least for raid 0 and 1 and combinations) is > often faster than what a hardware raid card can do, and almost certainly > better than what any fakeraid pulls off (since their drivers are often > crap at doing the raid in software). raid 5 on the other hand can often > be done faster by a dedicated xor engine, and since you don't have to do > as much reading to write you reduce bus bandwidth. Probably the main > advantage of hardware raid is reduced [b]us usage since only the actual > desired data goes over the bus, while with software raid, raid 1 > involves twice as much bus traffic to write to both devices.
If the raid card was PCI-e, would it matter? Worst case for the bus would be data to and from the drive's cache. For SATA-II, that's 300 MB/s. So to write to two drives at once it takes 600 MB/s. Since each lane of a PCI-e has a raw max rate of 250 MB/s, each drive needs two lanes to achieve this. So for a 5-port raid card, it would need to be x8 (300 MB/s x 5 / 250 MB/s = 6). Are they available? Or would there be contention within the north/south bridge where all the buss lanes meet? How do file servers address this? Doug. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]