[TriLUG] Ubuntu FakeRAID or Software

Brian Blater brb.lists at gmail.com
Mon Nov 8 13:29:46 EST 2010


On Sat, Nov 6, 2010 at 12:29 PM, Brian Blater <brb.lists at gmail.com> wrote:
> On Fri, Nov 5, 2010 at 10:32 PM, Rodney Radford <rradford at mindspring.com> wrote:
>>
>> As I mentioned earlier, when you create a new RAID, it starts off in a degraded state and is then rebuilt - possibly taking hours to complete.  It does this as it initially lists one of your drives as a spare, writing just to the other drives, and then incorporates the spare in during the rebuild.
>>
>> You can over-ride this as shown in this link:
>>
>> http://serverfault.com/questions/43575/how-to-create-a-software-raid5-array-without-a-spare
>>
>> -----Original Message-----
>>>From: Rodney Radford <rradford at mindspring.com>
>>>Sent: Nov 5, 2010 9:56 PM
>>>To: Triangle Linux Users Group General Discussion <trilug at trilug.org>
>>>Subject: Re: [TriLUG] Ubuntu FakeRAID or Software
>>>
>>>
>>>Did you examine /proc/mdstat before you rebooted? I suspect you were already in a degraded mode then as the system was still building the RAID. So when you rebooted, it started back again rebuilding the drive, you removed the drive (but it it still writing to it), so you get a busy when you try to add it back.
>>>
>>>Repeat the steps again, but this time check /proc/mdstat and verify it is complete (all UUUU) before the reboot. If you do happen to reboot before it is rebuilt, just be patient and wait for it to complete before changing it.
>>>
>>>Depending on the drive speed, RAID size, and RAID tuning parameters, it can take several hours for the initial build to complete.
>>>
>>>Also, check out this link for info on how to decrease the RAID rebuild time. I played with this about a year ago and was able to reduce a RAID rebuild on a 2TB array from several hours down to less than 30 minutes.
>>>
>>>http://www.ducea.com/2006/06/25/increase-the-speed-of-linux-software-raid-reconstruction/
>>>
>>>Good luck..
>
> Yes, After creating the RAID I run mdadm --detail /dev/md0 and waiting
> until everything was in sync. It showed the array to clean and
> everything sync'd. Only then did I format it and mount it as a test.
> Then when that all worked I rebooted.
>
> I'm not seeing anything particularly wrong in dmesg:
>
> [ 3100.990730] md: md0 stopped.
> [ 3101.150132] md: bind<sdd2>
> [ 3101.150364] md: bind<sde2>
> [ 3101.150646] md: bind<sdc2>
> [ 3101.208927] raid5: device sdc2 operational as raid disk 1
> [ 3101.208931] raid5: device sde2 operational as raid disk 3
> [ 3101.208935] raid5: device sdd2 operational as raid disk 2
> [ 3101.209617] raid5: allocated 4282kB for md0
> [ 3101.209664] 1: w=1 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
> [ 3101.209669] 3: w=2 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
> [ 3101.209673] 2: w=3 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
> [ 3101.209677] raid5: raid level 5 set md0 active with 3 out of 4
> devices, algorithm 2
> [ 3101.209697] RAID5 conf printout:
> [ 3101.209700]  --- rd:4 wd:3
> [ 3101.209703]  disk 1, o:1, dev:sdc2
> [ 3101.209705]  disk 2, o:1, dev:sdd2
> [ 3101.209708]  disk 3, o:1, dev:sde2
> [ 3101.209749] md0: detected capacity change from 0 to 112743677952
> [ 3101.209898]  md0: unknown partition table
>
> This just shows me it stopped the md0 and bound every disk in the RAID
> except sdb which is the disk in question.
>
> I see basically the same in /var/log/messages. In /var/log/daemon.log
> I see the following:
>
> Nov  5 20:26:18 porsche mdadm[1229]: DeviceDisappeared event detected
> on md device /dev/md0
> Nov  5 21:17:41 porsche mdadm[1229]: DegradedArray event detected on
> md device /dev/md0
>
> I think I'm going to rebuild this machine from scratch and see if
> there is anything different that happens.
>
> thanks,
> Brian
>

Well, I spent the weekend rebuilding the server and low and behold it
is working now. I've got one Array that is acting as my /home
directory and I'm working on a second Array to export as and AoE
device.

The only thing at this point that has me confused is after going into
fdisk or cfdisk and creating the partitions for the Array, I had to
reboot the machine to see the /dev/sdb# device. Is there something
special I need to do to get those devices written without a reboot? In
fdisk or cfdisk I wrote the changes to the drive.

Thanks again for everyone's help.

Brian



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