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Re: [dm-devel] - info about dm

Luca Berra wrote:
Anyway, I found a little problematic configuring it manually: I tried to
install SL5 on a node which was misconfigured: instead of seeing one
device, it was managing the 2 HD (/dev/sda and /dev/sdb) as 2 separate

This is as expected. The hardware is just a sata controller with two disks attached, so that is what the kernel sees. dmraid is used to recognize the bios information on the disk and configure the device mapper driver to create a raid virtual device.

devices an if I tried to configure them (at install time, via CD or
network boot) with  DM, I got many errors about the RAID table (“ERROR:
asr: Invalid RAID config table checksum on /dev/sda” or even “asr:
Invalid magic number in RAID table; saw 0x0 expected…”). I tried to
reconfigure the RAID card first via BIOS and then trying again to
configure it via Linux (“dmsetup create …”) but even if it seemed

dmsetup create creates a new dm device. Generally this command is for debugging and testing, so you should not use it. It has nothing to do with dmraid other than they are both clients of the device mapper kernel driver.

working (exit code 0), then querying the device asr_ (i.e. “dmraid –r”)
resulted in errors as reported above…or better, dmraid commands (-r,
-ay, -tay,…) reported errors, while dmsetup commands  (status, ls,…)

What where the exact commands and errors the generated?

I am also confused because the first thing you said was that the system DID correctly recognize the raid array as /dev/mapper/asr_xxxx.

2) Managing disks
I configured disks in RAID 1 (mirror) but I wonder how to manage this
RAID; in particular, how can I do for:
- stopping a device (disk) and put it offline/and viceversa? - reconfiguring/rebuilding it (due to broken/faulting HD)?
At the moment I should change a couple of disks (SMARTD warnings
reported), but I’m scared about the “RAID table error”…

Currently the only way is to do so in the bios. Some systems the bios will begin rebuilding when you tell it to, and you need to wait for it to finish. On others, it only marks the disk as needing rebuilt and relies on the windows driver to do the rebuilding. Currently dmraid does not perform rebuilding.

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