Hello, On 02/22/2011 05:16 PM, Hanspeter Kunz wrote: >> Persistence is not available for devices everywhere in the kernel. >> >> /dev/sd[??] >> Not persistent. They can change of reboots based on which one gets >> discovered first >> >> /dev/dm-* >> Not persistent. These are device mapper devices with the same caveat I >> mentioned above. >> >> /dev/disk/by* >> I don't know the history behind why it was started. But these entries >> are symlinks to block devices. Now when block devices are locked (like >> in your case), you can't use any of these entries. > > well, I guess the main idea of having /dev/disk/by-uuid is to have > persistence ;) >
Yes, indeed. But that is not to guarantee that the device is not locked. > I agree, during boot, when first the iscsi- and afterwards the > multipath-devices become available, these symlinks have to be changed. > This worked fine in lenny. If this really doesn't work anymore in sueeze > in principle (which I doubt) then this should at least be mentioned in > the NEWS such that people using it are informed. > > On the other hand, I still think that having the disk/by-uuid links for > the multipath devices would be nice, for various reasons. Most > importantly, because using the uuid *guarantees* that the system boots > the intended filesystem. Devices can change (e.g. in the case of iSCSI a > wrong device could be mapped to the machine, because of a configuration > error or whatever). Using uuid I would instantly realize that (because > the machine would not find the root fs). > > This worked on lenny and I would really like to have this feature again > in squeeze. > I have taken up the multipath-tools maintenance very recently. I can't really comment on what was in Lenny. But I can talk on multipath best practices. In multipath, you can disable "user_friendly_names", which will then give you access to the unique lun serial id based device names. The user_friendly_names was a [mis]feature IMO. So in simple, you can get the same guarantee with multipath also. >> /dev/mapper/* is the recommended way of using any Device Mapper >> solution. Be it linear, crypt, multipath, snapshot or anything else. > > I do not agree. All my debian systems (laptops with crypt, servers with > raid/lvm) boot with /dev/disk/by-uuid root devices. As far as I am > informed, this is also the debian default (when using grub). > by-uuid does not take care of block devices with no file systems. -- Ritesh Raj Sarraf | http://people.debian.org/~rrs Debian - The Universal Operating System
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