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I'm having a strange problem since I moved from Centos5 to Centos6. I have three disks, first two are used as a RAID1, and third one is a stand-alone backup disk that is not listed in /etc/fstab (it is mounded when needed and then unmounted).

My problem: After a boot, /dev/sdc exists but /dev/sdc1 does not. Also, the links in /dev/disks are also absent for the first partition of sdc. Disk itself is fine, and if I hot-remove it and plug it back in, /dev/sdc1 appears ok and everything is working.

My question: What subsystem manages auto-discovery of disks, partitions, etc. during the boot process (e.g. what creates /dev/disks/by-label)? How do I configure it to scan /dev/sdc too and create all relevant files and links in /dev ?

Edit: Here's the relevant part of dmesg output (the only place sdc appears). It does list sdc1, but it's not in /dev!

sd 1:0:0:0: [sdb] 1953525168 512-byte logical blocks: (1.00 TB/931 GiB)
sd 3:0:0:0: [sdc] 976773168 512-byte logical blocks: (500 GB/465 GiB)
sd 1:0:0:0: [sdb] Write Protect is off
sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sd 3:0:0:0: [sdc] Write Protect is off
sd 3:0:0:0: [sdc] Mode Sense: 00 3a 00 00
sd 3:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
 sdb:
 sdc:
sd 0:0:0:0: [sda] 1953525168 512-byte logical blocks: (1.00 TB/931 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
 sda:
DMAR:[DMA Read] Request device [00:1e.0] fault addr 361bc000 
DMAR:[fault reason 06] PTE Read access is not set
 sdb1 sdb2 sdb3
 sdc1
 sda1
sd 1:0:0:0: [sdb] Attached SCSI disk
sd 3:0:0:0: [sdc] Attached SCSI disk
 sda2 sda3
sd 0:0:0:0: [sda] Attached SCSI disk
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Is this raid-1 meant to be from mdadm, from motherboard fakeraid (dmraid) or real raid controller? Do you see the partitions on /dev/sdc with fdisk /dev/sdc and p ? What about /dev/sda and /dev/sdb ? fakeraid devices are now under /dev/mapper/ – anttir Nov 8 '11 at 17:19
/dev/sdc is not part of any RAID (just ext3 on top of /dev/sdc1), partitions are visible with fdisk. /dev/sda and sdb are part of mdadm raid (+lvm on top), and they are fine (everything is detected/mounted ok). – haimg Nov 8 '11 at 18:02
Weird. Can you see anything in dmesg that sheds any light? – Paul Nov 8 '11 at 22:33
I added the relevant part of dmesg... – haimg Nov 8 '11 at 23:06
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@anttir: Disk works ok once I do fdisk "w" and /dev/sdc1 appears... So I'm pretty convinced now it is an udev issue. But what exactly it is and how do I fix it? No idea... – haimg Nov 9 '11 at 6:31
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I had the same problem on Debian Squeeze and VMware disks, partitions for one disk were simply not in /dev, but they were visible by fdisk and in dmesg. I have upgraded udev package from 164 (found in stable) to 175 (found in testing) and after reboot everything works as it should.

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