On Saturday 21 March 2009 20:39:08 Jarry wrote: > Alan McKinnon wrote: > >> cp -a /mnt/gentoo/backup/var /mnt/gentoo/var > >> cp -a /mnt/gentoo/backup/usr /mnt/gentoo/usr > > > > Um, no. This gives you new usr and var directories like so: > > /usr/usr/ > > /var/var > > > > You want: > > cp -a /mnt/gentoo/backup/var /mnt/gentoo/ > > cp -a /mnt/gentoo/backup/usr /mnt/gentoo/ > > Thanks for correction! > > > With lvm, this becomes a breeze. > > I remember having lvm2 a few years ago, and despite of that I could not > extend any partition, which was being used. What is then lvm2 good for, > if I can not extend partitions on-the-fly? I can not unmount /usr before > extending...
That is not lvm's fault, it is the fault of the OS. /usr is not a filesystem that changes much anyway. If you look at a few similar machines, you can guess quite accurately what it's size is going to be. /var, database directories, home directories - these are the things you can change on the fly. These are also the things that you do want to change on the fly. > And one more counter-argument: with traditional partitions I can select > where a certain partition is (physically). Those partitions accessed > frequently I put to the beginning of the disk with higher transfer-rate. > In my case, it makes quite difference: > > obelix ~ # hdparm -t /dev/md2 > Timing buffered disk reads: 252 MB in 3.02 seconds = 83.23 MB/sec > > obelix ~ # hdparm -t /dev/md9 > Timing buffered disk reads: 150 MB in 3.02 seconds = 49.72 MB/sec You have no guarantee whatsoever that the data resides on the part of the disk you think it resides on, so this entire argument becomes moot. Today, by happy coincidence, it is. Tomorrow with another drive it might not be. You also have to deal with the effect of disk caching. And you didn't do the only real test the remotely means anything at all - random writes. Throughout measurements are meaningless as the thing you measure hardly ever happens in real life. It's a lot like determining the suitability of a future wife by measuring her foot size: a perfectly correct measure, and also a perfectly useless one. It's this kind of thinking that keeps people trapped in circumstance and unable to take advantage of new ideas. In the IT industry, it is rife. -- alan dot mckinnon at gmail dot com
