[dm-devel] - info about dm

[Phillip Susi]

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.