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On Mon, 20 Oct 2008 08:54:20 +0200 |
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Wolfgang Liebich <Wolfgang.Liebich@×××××××.com> wrote: |
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> Hi, |
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> |
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> <SNIP> |
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> > |
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> > the howtos on gentoo-wiki worked well for me. |
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> |
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> I'm working with them, too. Just one question remains: I want to use |
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> udev. Do I have to create the md devices or does udev that for me? |
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> |
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|
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udev will do it for you. But make sure your initramfs init script |
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unmounts /sys & /proc. On the box I'm working on setting up it |
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wasn't unmounting /sys on the initramfs, so when it switched to the |
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real root it thought /sys was already mounted & didn't mount /sys |
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under the real root, which meant that udev didn't work - which took |
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me a while to figure out. |
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|
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> > |
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> > |
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> > > - Put the root partition on another RAID1 (I thought about |
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> > > putting the root filesystem into my LVM setup, too -- it is |
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> > > REALLY annoying if the root partition get's to small), |
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> > |
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> > yeah, but if you have 20+ gb root is always big enough ;) AFAIK |
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> > lvm kills barriers. You use raid for better data security. So |
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> > using lvm is a bit.. contra productive. |
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> |
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> Sorry, I'm neither a LVM nor a RAID export - could you please |
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> elaborate on that? |
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> I like LVM because of the convenience it adds. |
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> |
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|
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Write barriers are a feature to allow write caching on the hard disks |
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w/out endangering filesystem integrity. Write caching helps |
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performance significantly, but also allows the disk to re-order write |
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requests - the disk may actually write a write-request that was |
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received later before a write-request that was received earlier, |
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which in some situations can lead to filesystem corruption. Write |
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barriers are a special type of request that the disk is not allowed |
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to reorder around - everything the disk receives before the write |
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barrier must be written before anything received after the write |
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barrier. But in order to work, write barriers need to be supported |
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by every layer from the filesystem down to the actual disk; if your |
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filesystem is on top of LVM & LVM doesn't support write barriers, |
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then you won't be able to use them, and if write caching is enabled |
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on the actual disks, you may be risking fileystem corruption. The |
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Device Mapper kernel subsystem (dm-crypt, dm-raid, LVM, etc.) does |
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not support write barriers - but neither does MD RAID except for |
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RAID1, so write caching is dangerous except for filesystems directly |
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on disk partitions or on RAID1 (if the RAID1 is directly on disk |
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partitions). |
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|
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I personally decided against using LVM because from what I read it's |
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difficult to correctly stripe-align LVM, and incorrect alignment can |
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have a very big performance impact. |
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|
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|
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Good luck, |
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Conway S. Smith |
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-- |
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The only "intuitive" interface is the nipple. After that, it's all |
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learned. (Bruce Ediger, bediger@××××××××.org, in comp.os.linux.misc, |
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on X interfaces.) |
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