Dear Benjamin, In message <52A9A1B3.5080706@xxxxxxxxxx> you wrote: > On several more RAID specific SoC (like the PowerPC 440x/460x) a XOR > engine is included to speed up RAID calculations (effectively a hardware > RAID engine). > > I think Intel Atom CPUs were planned/got a similar engine added, but > with the advance in CPU efficiencies and frequencies, these XOR engines > are practically obsolete: You will barely use 5% of your CPU (if a high > end CPU) for the parity calculation on RAID5. > > These days it seems that the overhead from the parity calculations are > so small that they become insignificant. I fully agree here. Even on a not so fresh desktop CPU (Intel Core2 Quad CPU Q9550 at 2.83GHz) I see this in the kernel logs: ... [ 15.944466] xor: measuring software checksum speed [ 15.983008] prefetch64-sse: 11592.000 MB/sec [ 16.020008] generic_sse: 10232.000 MB/sec [ 16.045623] xor: using function: prefetch64-sse (11592.000 MB/sec) ... So for each percent of CPU bandwith I offer I get 115 MB/s bandwith for parity calculations. None of the RAID arrays I have running would ever need even close to 10 % of my CPU (in theory, at least). Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@xxxxxxx I can't say I've ever been lost, but I was bewildered once for three days. - Daniel Boone (Attributed) -- 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
