On 08/10/2013 03:19 AM, John Strange wrote: > Yes, I think I do want to create partitions. My expectation is to create a > mapping based on one or more raw physical device (luns). There are a number > features I would like implement behind my mapping target driver. My > understanding is that I can treat the mapping (the target device) as if it were > a raw disk and that I can format it as appropriate for whatever workload will > use it. For typical uses you would format the raw physical device and then use the kpartx device-mapper application to create linear maps for each partition contained on the device. For e.g. this is how users work with partitions on multipath devices managed by multipath-tools and device-mapper. > For instance... I need to present a device (it would appear to the OS as a raw > block device) composed of ranges of blocks from different devices - spinning > media, ssd, PCIe flash, etc. My target driver can guarantee a QOS (throughput, > latency, combo) and it will service read requests across the range of physical > media comprising the target. > > This target device would appear to the OS as a block device. The workload that > uses the device might require a filesystem on it, so I need to mount a FS. Still not sure why you would want to place partitions on the linear maps but you can do it if you really want to: http://paste.fedoraproject.org/31461/76307438/ First example is creating and partitioning a linar mapping (I used a loop device as the backing but it will work with any block device). Following that is creating a file system on a partitioned linear device, and then on the whole linear device. There's no problem with either operation. > That's what I'm aiming for. I ran into problems trying to format my target > device so I created a linear mapping and it behaved the same way... could not > put a partition on it or format it. You do not need a partition to be able to format or use a device-mapper device - dm's devices do not support partitions (which is why you have to use the userspace kpartx - it reads partition tables and creates equivalend DM linear mappings for them). It sounds like something else is going on in your case - what errors do you get when you try to use the linear devices (busy for e.g.)? Regards, Bryn. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
