[lug] Mystery Disk Use, Fedora 23

stimits at comcast.net stimits at comcast.net
Sat Sep 24 07:32:07 MDT 2016

Thanks! This was the RAID info I needed, and you were right about the mirror rebuild....I should have thought of that, but the log was far back and I never saw it. Makes me wish I had a drive activity light for each drive, not just as a whole.
The iotop was exactly what I was looking for to figure out what is using disks. This would have figured out a lot of things very fast. What confuses me is that running fuser to find out who is using "/dev/md0" was showing nobody as touching it...all I can do is guess that kernel drivers not using anything in user space can't be seen by fuser, and perhaps the rebuild function is in kernel.
The "g<command>" stuff from BSD is not available, but knowing about config being embedded in the RAID device is useful.
I'm still wondering if anyone knows of a graphical LVM tool for Fedora 23? It seems system-config-lvm does not exist anymore.
----- Original Message -----From: Zan Lynx <zlynx at acm.org>To: Boulder (Colorado) Linux Users Group -- General Mailing List <lug at lug.boulder.co.us>Sent: Sat, 24 Sep 2016 04:08:20 -0000 (UTC)Subject: Re: [lug] Mystery Disk Use, Fedora 23

On 9/23/2016 9:06 PM, stimits at comcast.net wrote:> Hi,> I was planning on trying to make a RAID1 setup and then cover it with > LVM, but I only got as far as creating the RAID1 setup (it isn't > mounted, but I can verify I can format it or mount it, so on). Before > I created the RAID1 on two new disks there was nothing strange. After > I created this, I can see constant hard drive activity, it never ends. > It isn't updatedb, it isn't fsck.

Ah an easy one! This is almost certainly the MD driver running in the kernel, doing a RAID sync. You can use the drives while they synchronize, but the array won't be "clean" until it finishes. You should be able to view the status in /proc/mdstat if I remember that correctly.

It's all low priority disk IO and should not cause any problems. You can raise the disk IO priority if you want it to finish faster, although I don't remember the trick for that.

> I don't know how to remove my "/dev/md0" now that I've created it, but > I know I can't leave this constant hard drive access churning away, it > worries me (and I don't know which drive it is...I have many).Really, it shouldn't be a problem. It just takes a while to write 4 TB (or whatever you have) at low priority.> Is there something like top, but for watching disk I/O? I see nothing > using significant CPU, and I've tried fuser on any partition's device > special file which is not supposed to be mounted, and see nothing. > What is a good tool to find out what's is consuming disk activity?I like "atop" to see processes. I like "iostat -xk /dev/sd[a-z] 1' for just general IO stats.

> What is a good way to remove a RAID1 device (there is no > "/etc/mdadm.conf" and "/dev/md0" persists across boots).Use the mdadm tool I think. There isn't any file for it, the RAID layout is written onto the disks during setup.

--  Knowledge is Power -- Power Corrupts Study Hard -- Be Evil

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