[lug] more RAID0 on /

Lee Woodworth blug-mail at duboulder.com
Sat Nov 20 23:33:27 MST 2004

Maybe the thing to do is use a 3ware raid controller and take the raid 
management out of the kernel's hands.

>> I can't think of anything else that might be happening. From my dmesg 
>> (gentoo with udev and LVM, no initrd, no raidtools or raidstart):
>> ....
>> md: linear personality registered as nr 1
>> md: raid0 personality registered as nr 2
>> md: raid1 personality registered as nr 3
>> md: md driver 0.90.0 MAX_MD_DEVS=256, MD_SB_DISKS=27
>> device-mapper: 4.3.0-ioctl (2004-09-30) initialised: dm-devel at redhat.com
>> ....
>> md: Autodetecting RAID arrays.
>> md: autorun ...
>> md: ... autorun DONE.
> It does all this fine when I boot to IDE. If I use KRUD in rescue mode I 
> have to manually raidstart /dev/md0 first, it fails in that case to 
> autodetect (no errors given, it just doesn't seem to even try).
I would expect something like the first four md: lines even for a SCSI 
only system as they are status messages from the driver unreleated to 
any particular disk device. Does the rescue disk behave differently in 
IDE vs SCSI mode? If so then it may be something with the way the SCSI 
partitions are initialized or enumerated during the boot.

>> I am using LVM (which uses device mapper) so there are no raid arrays 
>> found. But the issues are the same, the /dev/md* devices need to be 
>> setup before the root fs mount.
> Just curious, is this LVM2? Initially I considered that probably just 
> RAID0 without LVM was simpler...I still believe that if I can't boot 
> RAID0 I won't be able to boot RAID0 inside of LVM, yet it might need 
> more user space tools in the initrd. The thing that worries me about 
> additional technologies like LVM or EVMS is that rescue might be 
> complicated by this, adding special requirements to rescue media.
LVMW2, which uses device mapper and and introduces additional 
complexity. A rescue CD would need to have the lvm2 tools on it. I think 
the gentoo live cds have the lvm tools and raidtools.

> D. Stimits, stimits AT comcast DOT net
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