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Old 01-30-2011, 07:37 PM
Les Mikesell
 
Default RHEL-6 vs. CentOS-5.5 (was: Static assignment of SCSI device names?)

On 1/30/11 1:37 PM, Chuck Munro wrote:
> Hello list members,
>
> My adventure into udev rules has taken an interesting turn. I did
> discover a stupid error in the way I was attempting to assign static
> disk device names on CentOS-5.5, so that's out of the way.
>
> But in the process of exploring, I installed a trial copy of RHEL-6 on
> the new machine to see if anything had changed (since I intend this box
> to run CentOS-6 anyway).
>
> Lots of differences, and it's obvious that RedHat does things a bit
> differently here and there. My focus has been on figuring out how best
> to solve my udev challenge, and I found that tools like 'scsi_id' and
> udev admin/test commands have changed. The udev rules themselves seem
> to be the same.

Do any of the names under /dev/disk/* work for your static identifiers? You
should be able to use them directly instead of using udev to map them to
something else, making it more obvious what you are doing. And are these names
the same under RHEL6?

--
Les Mikesell
lesmikesell@gmail.com
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Old 01-30-2011, 09:07 PM
Nico Kadel-Garcia
 
Default RHEL-6 vs. CentOS-5.5 (was: Static assignment of SCSI device names?)

On Sun, Jan 30, 2011 at 2:37 PM, Chuck Munro <chuckm@seafoam.net> wrote:
> Hello list members,
>
> My adventure into udev rules has taken an interesting turn. *I did
> discover a stupid error in the way I was attempting to assign static
> disk device names on CentOS-5.5, so that's out of the way.
>
> But in the process of exploring, I installed a trial copy of RHEL-6 on
> the new machine to see if anything had changed (since I intend this box
> to run CentOS-6 anyway).
>
> Lots of differences, and it's obvious that RedHat does things a bit
> differently here and there. *My focus has been on figuring out how best
> to solve my udev challenge, and I found that tools like 'scsi_id' and
> udev admin/test commands have changed. *The udev rules themselves seem
> to be the same.
>
> Regarding networking, all of my 'ifcfg-*' files from CentOS-5.5 worked
> well, including bridging for KVM. *Of course, one of the first things I
> did was remove that atrocious NetworkManager package ... it needs to be
> rewritten to make it a *lot* more intuitive. *RedHat uses it during
> installation to manually configure the NICs, which I think is a
> mistake. *I much prefer the way CentOS anaconda has done it so far, as a
> separate install menu form.

Unfortunately, working out all the dependencies and preventing it from
activation is more tricky. I suggest putting "NM_CONTROLLLED=no" in
all your /etc/sysconfig/network-scripts/ifcfg-* files, it just makes
the whole thing a lot safer for server class installations. I don't
know if it's more stable or workable in the latest Fedora releases,
but I'm still unhappy with it in CentOS and RHEL.

> The performance of the machine seemed to be better with the newer
> kernel, which is encouraging. *I suspect we can look forward to a number
> of improvements. *I've just managed to scratch the surface. *I do expect
> there may be a few challenges for those of us upgrading a system from
> 5.x to 6, where some user-written admin scripts could break depending on
> the system commands they use.

Ohhhhh, yes. This is inevitable with OS updates this far apart: just
the switch from the default sendmail and syslog to postfix and rsyslog
caught me somewhat by surprise.
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Old 02-02-2011, 10:57 PM
Chuck Munro
 
Default RHEL-6 vs. CentOS-5.5 (was: Static assignment of SCSI device names?)

On 02/02/2011 09:00 AM, Lamar Owen wrote:
>
> On Wednesday, February 02, 2011 02:06:15 am Chuck Munro wrote:
>> > The real key is to carefully label each SATA cable and its associated
>> > drive. Then the little mapping script can be used to identify the
>> > faulty drive which mdadm reports by its device name. It just occurred
>> > to me that whenever mdadm sends an email report, it can also run a
>> > script which groks out the path info and puts it in the email message.
>> > Problem solved:-)

> Ok, perhaps I'm dense, but, if this is not a hot-swap bay you're talking about, wouldn't it be easier to have the drive's serial number (or other identifier found on the label) pulled into the e-mail, and compare with the label physically found on the drive, since you're going to have to open the case anyway? Using something like:
>
> hdparm -I $DEVICE | grep Serial.Number
>
> works here (the regexp Serial.Number matches the string "Serial Number" without requiring the double quotes....). Use whatever $DEVICE you need to use, as long as it's on a controller compatible with hdparm usage.
>
> I have seen cases with a different Linux distribution where the actual module load order was nondeterministic (modules loaded in parallel); while upstream and the CentOS rebuild try to make things more deterministic, wouldn't it be safer to get a really unique, externally visible identifier from the drive? If the drive has failed to the degree that it won't respond to the query, then query all the good drives in the array for their serial numbers, and use a process of elimination. This, IMO, is more robust than relying on the drive detect order to remain deterministic.
>
> If in a hotswap or coldswap bay, do some data access to the array, and see which LED's don't blink; that should correspond to the failed drive. If the bay has secondary LED's, you might be able to blink those, too.
>
>

Well no, you're not being dense. It's a case of making the best of what
the physical hardware can do for me. In my case, the drives are
segregated into several 3-drive bays which are bolted into the case
individually, so removing each one to compare serial numbers would be a
major pain, since I'd have to unbolt a bay and remove each drive one at
a time to read the label.

The use of the new RHEL-6/CentOS-6 'udevadm' command nicely maps out the
hardware path no matter the order the drives are detected/named, and
since hardware paths are fixed, I just have to attach a little tag to
each SATA cable with that path number on it. One thing I did was reboot
the machine *many* times to make sure the controller cards were always
enumerated by Linux in the same slot order.

I also notice that the RHEL-6 DriveInfo GUI application shows which
drive is giving trouble, but it only maps the controllers in a vague way
with respect to the hardware path. (At least that's what I remember
seeing a couple of days ago, I could be mistaken.)

On this particular machine I don't have the luxury of per-drive LED
activity indicators, so whacking each drive with a big read won't point
the way (but I have used that technique on other machines). I didn't
have the funds to buy the hot-swap bays I would have preferred. I may
retrofit later.

Your suggestions are well taken, but the hardware I have doesn't readily
allow my use of them. Thanks for the ideas.

Chuck
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