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