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Old 06-08-2017, 02:50 AM   #1
monojeffrey
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Redhat Server and Provisioning Storage to it


Hi ,

This is actually a interview question and important activity from server side

How to provision a LUN once the WWN number is shared to us from storage team??(physical servers)

Steps normally would be to scan the interfaces in directory
/sys/class/scsi_host/host()

(0,1,2,3)nomrally numbers etc...
and check the availability of new LUNS using multipath -ll (if multiple paths are used)

sometimes the lun wont get detected after several scanning
but we can identify the LUN once the server is rebooted

Question is, If there is any methods or procedures without the REBOOT
 
Old 06-08-2017, 08:16 AM   #2
MensaWater
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In /etc/multipath.conf you have to make sure the array type is not blacklisted and better yet you should add a definition based on the disk array manufacturer's recommendations.

Typically I install the sg3_utils and lsscsi RPMs from the RedHat repositories.

I run the rescan-scsi-bus.sh that comes from sg3_utils and only try other scan types if that fails.

lsscsi command will show all your SCSI devices (/dev/sd*) individually.

Multipath only shows devices if it determines it should be under multipath setup (which can be for single path) The "multipath" device can be comprised of a single sd device if there are no other paths found. I recommend doing multipath setup even for single paths presented to host because if you use the "multipath" device (e.g. friendly name /dev/mapper/mpath*) in your LVM VG setups or Oracle ASM setups or whatever else you're doing it allows for future changes. (e.g. If you move from one switch to another but are still using the same array the UUID of the disk is the same and your multipath will include the sd it sees from new switch. If you didn't use multipath initially you'd have to modify your underlying VG or ASM Volume or whatever to use the new sd.)

If the rescan doesn't find it then there are other ways to scan.

If you're using Qlogic fiber HBAs you can determine which host# devices under /sys/class/scsi_host are your Qlogic by running: grep -i ql */* 2>/dev/null"
Once you know which host# those are you can force each to rescan by running:
echo "- - -" host#/scan

Another tool is offered by Qlogic to work with their HBAs and you can download it from their site. It's called the Qlogic-SuperInstaller and they have one for RHEL. With it you can use the qaucli command to view details. The download package also includes a rescan utility you can use.

I don't work with Emulex so can't comment them much.
 
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Old 06-09-2017, 04:13 AM   #3
voleg
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HOWTO LUNs on Linux using native tools
 
Old 07-12-2017, 11:14 AM   #4
Tim Walsh
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Question rescanning SCSI Bus

SO I found myself with a new job in a mixed windows / Linux environment where previously I was working primarily with Windows.

I have a redhat 5.11 failover cluster hosting (clustered) Oracle. The cluster has been up several years, but we recently added more storage to the shared enclosure. I've presented the storage to both hosts and (Like Windows) the next step would be to partition, format / mount, etc.

I ran fdisk -l and the drives are not listed so (like this thread indicates) I can rescan the SCSI bus in order to detect the new drives without having to reboot. Windows disk administrator does that fine, but their stupid "cluster readiness wizard" will offline ALL the drives if you don't de-select storage before running it. (imagine that!)

If I run the "rescan the SCSI Bus" script, that does not take any drives offline does it? And, I've read there is extra foo and love the drives need for Oracle to like them, but I can work with the DBAs on that end. I think I just need to rescan the bus, partition and write a file system to it, and I'm golden.

Thanks!

Tim
 
Old 07-13-2017, 08:50 AM   #5
MensaWater
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You should start a new thread to ask your questions. It gets higher visibility.
 
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Old 07-13-2017, 09:38 AM   #6
Tim Walsh
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Thanks!

yes, I was actually thinking that after I posted. I'll do that.

I appreciate the help!

Tim
 
Old 07-15-2017, 06:53 PM   #7
Laserbeak
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That's a crazy interview question, unless you do it everyday, it's something anyone would have to look up.

When I was in the position to interview candidates (but I was never in the position to make the final decision), I tried to do all I could to make sure I never asked these gotcha questions.

Last edited by Laserbeak; 07-15-2017 at 06:55 PM.
 
Old 07-18-2017, 08:40 AM   #8
MensaWater
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Quote:
Originally Posted by Laserbeak View Post
I tried to do all I could to make sure I never asked these gotcha questions.
Sometimes you ask questions to see how people think and respond. If someone says "I don't know, I've never done that" it is almost as valuable as hearing them spell it out from top to bottom. I'd much rather have someone honestly tell me they don't know than try to pretend they've done it when they haven't.

I used to ask people if they took geometry in high school or college not because they needed it for the job but because I knew one of the first things they teach in geometry is logic and syllogisms. The look on their faces when I asked this seemingly non sequitur was amusing.

Of course I did get a question once that to this day I'm sure I answered "wrong" but don't know what the interviewer thought was "correct": "What is different about RedHat Linux than every other Linux?"
I know of many things that are different and gave them all when it was clear I wasn't giving the answer he wanted. More than 10 years later I still have no clue what he wanted even though I've been working on RedHat all that time.
 
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