On Wed March 22 2006 11:28 pm, Joseph Yasi wrote: > I am using the dmraid utility to detect and configure my Intel > Software Raid RAID0 array. When upgrading to 2.6.16 from 2.6.15, the > system failed to boot because the device-mapper array was not built. > I have traced the problem to this patch that limits dm-stripe to > targets that are multiples of the chunk size. I don't know whether to > consider this a problem with device-mapper or with the Intel Software > Raid BIOS that built the array. Dmraid is giving me a target of > 980460038 blocks with a chunk size of 256 blocks. Is this a problem > with device-mapper, the dmraid utility or the raid bios? Should > device-mapper handle striped targets that are not multiples of the > chunk size? Hmm...I obviously didn't expect dmraid to be creating such devices. The kernel patch that was added to 2.6.16 is definitely correct. Dm-stripe should not allow creating a device with a size that's not a multiple of the chunk-size. To do so leaves a partial chunk at the end of each device. While at first glance this might not seem like a big deal, the striping calculations in the I/O path do not handle this situation (at least, not in the way you would think it should be handled), and cause I/O errors if you try to access the end of the stripe device. > dmesg gives these pertinent lines: > device-mapper: dm-stripe: Target length not divisible by chunk size. > device-mapper: error adding target to table. > > dmsetup status > isw_caejhbcidd_Volume03: 0 976173660 linear > isw_caejhbcidd_Volume02: 0 4209030 linear > isw_caejhbcidd_Volume01: 0 64197 linear > isw_caejhbcidd_Volume0: 0 980460038 striped > > dmraid -s > *** Group superset isw_caejhbcidd > --> Active Subset > name : isw_caejhbcidd_Volume0 > size : 980460038 > stride : 256 > type : stripe > status : ok > subsets: 0 > devs : 2 > spares : 0 In your example, your stripe device is 980460038 sectors, with a 256 sector chunk-size.This means the stripe device has 3829922 chunks, with 6 sectors left over (3 on each of the two devices, presumably). I would think that the BIOS intends that these last 3 sectors on each device should be striped with an effective chunk-size of 3 sectors. To do this, dmraid should set up a device with two targets, one with a chunk-size of 256, and one with a chunk-size of 3. The map would look something like: 0 980460032 striped 2 256 /dev/hda 0 /dev/hdb 0 980460032 6 striped 2 3 /dev/hda /dev/hdb 490230016 Unfortunately, this doesn't work either, because the chunk-size must be a power-of-2. So...since we know the second target in the map really represents only one "stripe", we could treat them as a concatenation of independent linear targets. So we end up with a map like this: 0 980460032 striped 2 256 /dev/hda 0 /dev/hdb 0 980460032 3 linear /dev/hda 490230016 980460032 3 linear /dev/hdb 490230016 I'm thinking that this mapping would do what the BIOS is actually intending. It ought to be relatively straight-forward to recognize this situation in dmraid and set up a mapping similar to the one above. -- Kevin Corry kevcorry@xxxxxxxxxx http://www.ibm.com/linux/ http://evms.sourceforge.net/ -- dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
