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On Montag 20 Oktober 2008, Conway S. Smith wrote: |
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> On Mon, 20 Oct 2008 08:54:20 +0200 |
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> |
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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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> udev will do it for you. But make sure your initramfs init script |
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> unmounts /sys & /proc. |
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|
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just don't use an initramfs/initrd. |
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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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> 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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also, reiserfs and xfs turn barriers on by default, ext3 turns it off per |
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default. Because of 'performance reasons'. |
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