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