looks good i'd like to see the 2.4 kernel patches as well Could you post them at parisc-linux.org ? On Fri, 2003-08-29 at 08:41, Paul Clements wrote: > At long last... I've finally got my additions to Peter T. Breuer's raid1 > bitmap code (fr1 v2.14, ftp://oboe.it.uc3m.es/pub/Programs/fr1-2.14.tgz) > in decent shape and fairly well tested. > > The bitmap and asynchronous write capability are primarily useful when > raid1 is employed in data replication (e.g., with a remote disk served > over nbd as the secondary device). However, the bitmap is also useful > for reducing resync times with ordinary (local) raid1 and raid5 arrays. > > The additions, above and beyond the original fr1 code, are basically: > > * disk storage for the bitmap (makes the bitmap persistent, so that a > full resync is never needed, even after a failure or reboot of the > primary server) > > * a kernel daemon to periodically (lazily) clear bits in the bitmap file > (this reduces the number and frequency of disk writes to the bitmap > file) > > * changing bits in the bitmap to 16-bit counters (this ensures that a > bit won't be cleared prematurely when there are multiple outstanding > I/Os to a block, which could result in data loss on the backup system if > a failure coincided) > > * allowing the bitmap to be rescaled -- i.e., changing the amount of > data that each bit represents (currently, the 2.6 code can handle a > chunk size up to 64k) > > * modifying the code so that it can be more easily leveraged by other > raid drivers (namely raid5) > > I originally wrote this code for 2.4 (I have a patch vs. 2.4.19 SuSE > kernel, if anyone is interested) and recently ported it to 2.6. The code > currently allows the use of a bitmap with raid1 arrays (this could also > be extended to raid5, but I haven't put the bitmap calls into raid5.c -- > if anyone would like to do that, I'd love to see it happen -- it > shouldn't be hard if you're familiar with raid5 (...I'm not :/). > > > I have also modified Neil's mdadm tool to allow it to configure the > additional bitmap and async parameters. The attached patch is against > the 1.2 mdadm release. Briefly, the new options are: > > Creation: > > mdadm -C /dev/md0 -l 1 --persistent > --bitmap=/tmp/bitmap_md0_file,65536,15 --async=512 -n 2 /dev/xxx > /dev/yyy > > This creates a raid1 array with: > > two disks > a persistent superblock > asynchronous writes enabled (maximum of 512 outstanding writes) > bitmap enabled (using the file /tmp/bitmap_md0_file) > a bitmap chunksize of 64k (bitmap chunksize determines how much data > each bitmap bit represents) > the bitmap daemon set to wake up every 15 seconds to clear bits in the > bitmap file (if needed) > /dev/xxx as the primary disk > /dev/yyy as the backup disk (when asynchronous writes are enabled, the > second disk in the array is labelled as a "backup", indicating that it > is remote, and thus no reads will be issued to the device) > > > Assembling: > > mdadm -A /dev/md0 --bitmap=/tmp/bitmap_md0_file /dev/xxx /dev/yyy > > This assembles an existing array and configures it to use a bitmap file. > The bitmap file pathname is not stored in the array superblock, and so > must be specified every time the array is assembled. > > > Details: > > mdadm -D /dev/md0 > > This will display information about /dev/md0, including some additional > information about the bitmap and async parameters. > > > I've also added some information to the /proc/mdstat file: > > # cat /proc/mdstat > Personalities : [raid1] > md1 : active raid1 loop0[0] loop1[1](B) > 39936 blocks [2/2] [UU] > async: 0/256 outstanding writes > bitmap: 1/1 pages (15 cached) [64KB], 64KB chunk, file: > /tmp/bitmap_md1 > > unused devices: <none> > > > Finally, the patches are available here: > > kernel patch vs. 2.6.0-test3: > > http://parisc-linux.org/~jejb/md_bitmap/md_bitmap_2_28_2_6_0_TEST3.diff > > mdadm patch vs. 1.2.0: > > http://parisc-linux.org/~jejb/md_bitmap/mdadm_1_2_0.diff > > > So if you have any interest, please review, test, ask questions, etc. > > (And if you're really a glutton, the gory details of the design and > implementation can be found in Section 3 of my OLS Paper: > http://archive.linuxsymposium.org/ols2003/Proceedings/All-Reprints/Reprint-Clements-OLS2003.pdf) > > > Thanks, > Paul > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
