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[dm-devel] - info about dm



Dear all,

 

I just installed Scientific Linux 5 and I used for the first time DM drivers for working with the embedded RAID (the servers are IBM xSeries, with an Adaptec HostRAID ASR - SATA). I really appreciate the fact that now Linux is able to recognize such devices, but I had some troubles configuring it and I’d like to have some info for better understanding how things work.

 

I’ll be a little “verbose” for clarifying what I did and which are my doubts…

 

1)       Installation & Configuration

 

I installed SL5 on a system which was running SL3 with HW drivers released by IBM. Linux was able to identify correctly the device (installed through CD), mapped it as /dev/mapper/asr_ and proceeded with he installation.

 

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 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 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,…) worked normally. The only way I found for well-configuring the device was to install SL3 with specific drivers, and then to install SL5 with DM…all both commands now work perfectly

 

In brief:

If I try to configure DM-RAID from scratch and I get such errors, how can I do? What’s that “RAID table”? Where is it written? Not in the MBR of an HD, ‘cause I tried to copy the MBR of the cloned disk which had no problem (still recognized as “good” for RAID and DM) and nothing changed…

 

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”…

 

 

Many Thanks in advance for all help you can give me…

 

Best Regards

 

Vega Forneris

 

+--------------------------------------+

 Vega Forneris


 CNR – Servizi Informatici di Campo

 Gestione servizi GRID


 Area di Ricerca Roma II - Tor Vergata
 Via del Fosso del Cavaliere, 100
 00133 Roma


 Tel:   +39 06 4993 4667

 Fax:   +39 06 4993 4650

 Email: Vega Forneris sic rm cnr it

+--------------------------------------+

 

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