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Re: [dm-devel] md_component_detection = 1

All I can comment is LVM over the multipath implementation from Alasdair, RedHat.

For that, you need to set in /etc/lvm/lvm.conf :

scan = [ "/dev", "/dev/mapper" ] (you may or may not need this one, depending on your distro)
filter = [ "r/sd.*/", "a/.*/" ]
types = [ "device-mapper", 254 ]

Here the 254 may vary depending on your setup. To find out for your case, do :

[root cl039 root]# grep mapper /proc/devices
254 device-mapper

Then everything should work as expected :

[root cl039 root]# multipath -l -v2
red (3600a0b80000b596a000003113d9c5381)
[size=33 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [enabled][first]
 \_ 4:0:3:9 sdan 66:112  [ready ][active]
 \_ 5:0:1:9 sdbh 67:176  [ready ][active]
\_ round-robin 0 [enabled]
 \_ 5:0:3:9 sdcb 68:240  [ready ][active]
 \_ 4:0:1:9 sdt  65:48   [ready ][active]

[root cl039 root]# pvcreate /dev/mapper/red
 Physical volume "/dev/mapper/red" successfully created

[root cl039 root]# pvscan
 PV /dev/mapper/red         lvm2 [33.86 GB]
 Total: 1 [33.86 GB] / in use: 0 [0   ] / in no VG: 1 [33.86 GB]

That's the more precise info I can share onn the subject. Now your on your own.


shahid shaikh wrote:

Hello Chris,

   I have written a sample psuedo driver which is basically consolidating
multiple paths to LUNs.
So I need prevent SCSI devices from scanning.

I gone thro' lvm.conf and found out that md is doing the similar thing by
setting following value in lvm.conf

        md_component_detection = 1
this parameter, if set, prevents scanning of all the SCSI devices
contributed in the creation of md.

So is there any parameter in LVM2 or device mapper, setting or clearing
which can prevent scanning of SCSI devices used for my psuedo driver.
Obviously other than filtering it out.

Thanks and Regards,
Shahid Shaikh.
Software Engineer.

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