That is typically 100MB/sec per disk as it is reported, and that is a typical speed I have seen for a rebuild and/or grow. There are almost certainly algorithm sync points that constrain the speed less than full streaming speed of all disks. The algorithm may well be, read the stripe, process the stripe and write out the new stripe, and start over (in a linear manner) I would expect that to be the easiest to keep track of, and that would roughly get your speed (costs a read to each old disk + a write to the new disk + bookkeeping writes + parity calc). Setting up the code such that it overlaps the operations is going to complicate the code, and as such was likely not done. And regardless of the client's only being able to run raid5, there is significant risks to running raid5. If on the rebuild you find a bad block on one of the other disks then you have lost data, and that is very likely to happen--that exact failure was the first raid failure I saw 28+ years ago). How often are you replacing/rebuilding the disks and why? On Fri, Jan 14, 2022 at 8:10 AM Jaromír Cápík <jaromir.capik@xxxxxxxx> wrote: > > Hello Roger. > > >> Also, grow differs in the fact that blocks get moved around hence the writes. > > > > Of course, but even of that the speed was poor :] > > Just for info, I just tried to DD data on the second (faster) hardware > from one RAID drive to an empty one with MD offline and the transfer > speed is the following (sorry for the czech locale :) ... > > 25423+0 záznamů přečteno > 25422+0 záznamů zapsáno > 26656899072 bajtů (27 GB, 25 GiB) zkopírováno, 105,227 s, 253 MB/s > 25903+0 záznamů přečteno > 25902+0 záznamů zapsáno > 27160215552 bajtů (27 GB, 25 GiB) zkopírováno, 107,235 s, 253 MB/s > 26386+0 záznamů přečteno > 26385+0 záznamů zapsáno > 27666677760 bajtů (28 GB, 26 GiB) zkopírováno, 109,245 s, 253 MB/s > > as you can see, the write speed really matches the speed from the drive datasheet, > so ... why the sync speed was 100MB/s only when the CPU load was low? > Can you explain that? > > Thanks, > Jaromir
