Thank you, Andy.

I tried to apply the patch you guys mentioned by compiling the module following instructions at http://wiki.centos.org/HowTos/BuildingKernelModules#head-d2e4c05886f94c701e4ae74387d41d8c40c25d01, but it didn't work.

I've been struggling with it for the last 8 hours and no luck so far.

I really don't know what's wrong. I'm not a linux kernel developer and I'm most likely failing because of something stupid.

I know this must not the right place to ask for help on such matters, but if you guys could shed some light here, I'd really appreciate that.

Well, if you're up to it, here's the situation:

Looks like the module compilation worked (no errors or warnings occurred when I followed the instructions at the centos wiki), but I'm unable to load the new module to my running kernel.

I even copied the compiled and patched module to /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/ (overwrote the original) and /lib/modules/2.6.32-279.19.1.el6.x86_64/extra and rebooted the instance...

Also, dmesg does not complain about a thing...

# modinfo /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/xen-blkfront.ko

filename: /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/xen-blkfront.ko

alias: xenblk

alias: xen:vbd

alias: block-major-202-*

license: GPL

description: Xen virtual block device frontend

srcversion: B00B4183E470515A96DA320

depends:

vermagic: 2.6.32-279.19.1.el6.x86_64 SMP mod_unload modversions

parm: sda_is_xvda:sdX in guest config translates to xvdX, not xvd(X+4) (bool)

# uname -r

2.6.32-279.19.1.el6.x86_64

I also tried to remove the module and insert the patched one with insmod, but modprobe and rmmod are unable to unload it. They say it's in use.

# lsmod |grep blkfront

xen_blkfront 15495 1

I don't know what this "1" stands for, but if I were to guess, I'd say it's something unremovable...

Please let me know if you need any other information.

Thanks,

Luis Alen

www.izap.com.br
Ligue com tarifa local de todo o Brasil 4020.3000

On Tue, Jan 15, 2013 at 4:13 PM, Andy Grimm <agrimm@gmail.com> wrote:

See https://bugzilla.redhat.com/show_bug.cgi?id=729586

On Tue, Jan 15, 2013 at 1:10 PM, Luis Fernando Alen <luis.alen@izap.com.br> wrote:

Hello, list.

Yesterday I was pleased to see that Centos has released official images at the aws marketplace. Nice job.

Today I started playing with the Centos 6.3 image (https://aws.amazon.com/marketplace/pp/B00A6L6F9I, on which I plan to deploy a gluster cluster in production soon) and noticed a weird thing.

EBS Volumes attached to sd<X> are translated to xvd<Y> at the OS level. However, after a few research and IRC chat, I figured out that it's not weird, it's actually a normal and expected behavior (thanks for your help, z00dax).

sdX is actually mapped to xvdX+4. There is a consistent offset of 4. Suppose you attach an ebs volume to /dev/sdf. It'll be translated to xvdj at the OS level. sdg to xvdk, sdh to xvdl and so on.

Allright. After having figured the mystery out, it became easy to work on automations that deal with ebs volumes and file systems, such as volumes created, attached and mounted on the fly, snapshots that freeze file systems and so on...

However, I really do think to myself: Wouldn't it be cleaner if the image use simple translation (sdX to xvdX)? If I'm not wrong, Rightscale uses this on their Centos images and it's much simpler. There's no extra work needed to deal with that 4 offset when you want to automate things.

Is there a reasonable reason for the 4 offset which makes it unchangeable?

It's just a thought. I think it's worth considering it..

Luis Alen
www.izap.com.br
Ligue com tarifa local de todo o Brasil 4020.3000

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