Messages in this thread | | | From | Felix Bellaby <> | Subject | RAID10 overwrites partition tables | Date | Fri, 26 Nov 2004 18:23:58 +0100 (CET) |
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mdadm --level 10 does not seem to respect disk partition boundaries.
Whilst trying to construct a small RAID10 array on a workstation, I naturally attempted to set the array up over partitions to leave somewhere for grub to access the kernel. Using partitions also assists with booting Fedora 3 as it relies on RAID autodetection and partition labels in its standard initial ram disk.
However, the RAID10 seems to overwrite some of the partition tables.
For example, configuring a RAID10 array over 3 partitions as follows:
mdadm --create /dev/md0 --level 10 --raid-devices 3 \ /dev/sda1 /dev/sdb1 /dev/sdc1
seems to overwrite the partition tables for the disks in the same way as configuring RAID10 over the complete disks:
mdadm --create /dev/md0 --level 10 --raid-devices 3 \ /dev/sda /dev/sdb /dev/sdc
A more detailed example:
echo ',,fd' | sfdisk /dev/sda echo ',,fd' | sfdisk /dev/sdb echo ',,fd' | sfdisk /dev/sdc
mdadm --create /dev/md0 --level 10 --raid-devices 3 \ /dev/sda1 /dev/sdb1 /dev/sdc1
mke2fs /dev/md0
sfdisk -d /dev/sda sfdisk -d /dev/sdb sfdisk -d /dev/sdc
One of the partition tables in the above example will be replaced with the start of the second chunk of the ext2 fs, just as one would expect with an array configured over /dev/sda, dev/sdb and /dev/sdc.
The problem appears consistently on my test system (minimal Fedora 3 on an NForce3 system using the sata_nv.ko device driver). I have had the same results with a separate, identical system, and when using various custom 2.6.9 kernels. However, the problems do not appear with RAID5.
The code in raid10.c is probably to blame. A cursory examination suggests that raid10.c accesses the configured devices using very similar code to raid1.c (where the problem might go unnoticed) but rather differently from raid5.c.
Felix
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