[dm-devel] - info about dm
Vega Forneris
vega.forneris at sic.rm.cnr.it
Wed Nov 7 13:51:52 UTC 2007
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 Id like to have some info for better understanding
how things work.
Ill 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
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? Whats 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 Im 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 at sic.rm.cnr.it
+--------------------------------------+
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