On Thursday December 15, Robert.Heinzmann@xxxxxxx wrote: > Hello, > > i just downloaded the mdadm 2.2 version. It seems that there are some > new options which are not explained in details. of special interest are > 2 options. > > -GROW > The new grow mode is very very helpfull for us. It would allow us to do > resize operations with md devices at last - without the need for LVM. > The manpage states that the GROW mode requires kernel support to work. > There is no note that states, which kernel supports the options. Also > with various distributions with patched kernels its not possible to say > version X.Y.Z. of the kernel contains the required patches. > > Is there a way to find out via mdadm, if the current kernel supports the > GROW mode, prior to performing the GROW ? No, there isn't. However if your kernel doesn't support the operation, it will fail cleanly so there is no risk. > > -bitmap > > As far as I understand this bitmap options, in incorperates write intend > logging. > Is this based on paper by James Bottomley ? Also is there a way to find > out via mdadm if the running kernel supports intend logging via > mdadm ? Yes, it is comes (indirectly) from James. No, you cannot query the kernel. > > -There is also an option --write-mostly since 2.0. > > I guess this especially usefull for MD devices with large storage arrays > as backend. They have clever caches and read ahead paramaters, that can > be non-effective if we change the disk for each read. Does this option > require a kernel modification too ? Yes, this also requires a recent kernel - 2.6.14 I think. It is intended for mirrored situations where one mirror is over a slow link (e.g. over the Internet). . > > One last question. Besindes the source code and manpage is there oterh > documentation available on how the md works internally ? (update of > superblock, handling of device renaming inside the superblock etc.) No there isn't, though I am seeing more and more requests for this and am starting to wonder if I should commit some time to writing something. 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
