On Mon, January 5, 2009 1:45 pm, Martin K. Petersen wrote: >>>>>> "John" == John Robinson <john.robinson@xxxxxxxxxxxxxxxx> writes: > > John> Essentially DIF on 32k blocks instead of 512 byte ones. But > John> perhaps this is a bad assumption and MD/DM already optimises out > John> whole-chunk reads and writes where they're not required (for very > John> short, less-than-one-chunk transactions), and I've no idea whether > John> this happens a lot. > > I haven't looked at the RAID4/5/6 code for a long time so I'm not sure > whether they only write dirty pages or the whole chunk + parity ditto. > Neil? md/RAID456 writes whole pages (aligned to the array) but not whole chunks. If a filesystem request to write one page which is at a sector address which is not a multiple of the page size, we will pre-read the read of the two array-aligned pages, and when write them (and parity) back out. Otherwise, it will just write the requested pages plus parity updates. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
