Raid array is not automatically detected.

Raid array is not automatically detected.

[Bryan Christ]

My apologies if this is not the right place to ask this question. 
Hopefully it is.

I created a RAID5 array with:

mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
/dev/sdc1 /dev/sdd1 /dev/sde1

mdadm -D /dev/md0 verifies the devices has a persistent super-block, but 
upon reboot, /dev/md0 does not get automatically assembled (an hence is 
not a installable/bootable device).

I have created several raid1 arrays and one raid5 array this way and 
have never had this problem.  In all fairness, this is the first time I 
have used mdadm for the job.  Usually, I boot to something like 
SysRescueCD, used raidtools to create my array and then reboot with my 
Slackware install CD.

Anyone know why this might be happening?

Bryan

Re: Raid array is not automatically detected.

[Zivago Lee]

On Fri, 2007-07-13 at 15:36 -0500, Bryan Christ wrote:
> My apologies if this is not the right place to ask this question. 
> Hopefully it is.
> 
> I created a RAID5 array with:
> 
> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
> /dev/sdc1 /dev/sdd1 /dev/sde1
> 
> mdadm -D /dev/md0 verifies the devices has a persistent super-block, but 
> upon reboot, /dev/md0 does not get automatically assembled (an hence is 
> not a installable/bootable device).
> 
> I have created several raid1 arrays and one raid5 array this way and 
> have never had this problem.  In all fairness, this is the first time I 
> have used mdadm for the job.  Usually, I boot to something like 
> SysRescueCD, used raidtools to create my array and then reboot with my 
> Slackware install CD.
> 
> Anyone know why this might be happening?

Are you trying to boot on this raid device?  I believe there is a
limitation as what raid type you can boot off of (IIRC. only raid0 and
raid1).

-- 
Zivago Lee <z@ziff.net>

Re: Raid array is not automatically detected.

[Bryan Christ]

I would like for it to be the boot device.  I have setup a raid5 mdraid 
array before and it was automatically accessible as /dev/md0 after every 
reboot.  In this peculiar case, I am having to assemble the array 
manually before I can access it...

mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1

Unless I do the above, I cannot access /dev/md0.  I've never had this 
happen before.  Usually a cursory glance through dmesg will show that 
the array was detected, but not so in this case.

Zivago Lee wrote:
> On Fri, 2007-07-13 at 15:36 -0500, Bryan Christ wrote:
>> My apologies if this is not the right place to ask this question. 
>> Hopefully it is.
>>
>> I created a RAID5 array with:
>>
>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
>> /dev/sdc1 /dev/sdd1 /dev/sde1
>>
>> mdadm -D /dev/md0 verifies the devices has a persistent super-block, but 
>> upon reboot, /dev/md0 does not get automatically assembled (an hence is 
>> not a installable/bootable device).
>>
>> I have created several raid1 arrays and one raid5 array this way and 
>> have never had this problem.  In all fairness, this is the first time I 
>> have used mdadm for the job.  Usually, I boot to something like 
>> SysRescueCD, used raidtools to create my array and then reboot with my 
>> Slackware install CD.
>>
>> Anyone know why this might be happening?
> 
> Are you trying to boot on this raid device?  I believe there is a
> limitation as what raid type you can boot off of (IIRC. only raid0 and
> raid1).
> 

Re: Raid array is not automatically detected.

[Bill Davidsen]

Bryan Christ wrote:
> My apologies if this is not the right place to ask this question. 
> Hopefully it is.
>
> I created a RAID5 array with:
>
> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
> /dev/sdc1 /dev/sdd1 /dev/sde1
>
> mdadm -D /dev/md0 verifies the devices has a persistent super-block, 
> but upon reboot, /dev/md0 does not get automatically assembled (an 
> hence is not a installable/bootable device).
>
> I have created several raid1 arrays and one raid5 array this way and 
> have never had this problem.  In all fairness, this is the first time 
> I have used mdadm for the job.  Usually, I boot to something like 
> SysRescueCD, used raidtools to create my array and then reboot with my 
> Slackware install CD.
>
> Anyone know why this might be happening? 

Old type arrays are assembled due to having the proper partition type, 
0xfd "Linux auto RAID" and are assembled by the kernel. All others are 
assembled by mdadm running out of initrd or similar, and failures there 
result from not having a proper config file in the initrd image.

IIRC raidtools does set the array partitions to the auto-assemble 
partition type. Hope that points you in the right direction. Running
    "fdisk -l"
as root will let you see all the partitions, types, etc, for everything 
on your system.

I may be wrong, I thought auto-assemble only worked with type 0 or 1.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: Raid array is not automatically detected.

[Justin Piszcz]

On Sat, 14 Jul 2007, Bill Davidsen wrote:

> Bryan Christ wrote:
>> My apologies if this is not the right place to ask this question. Hopefully 
>> it is.
>> 
>> I created a RAID5 array with:
>> 
>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
>> /dev/sdc1 /dev/sdd1 /dev/sde1
>> 
>> mdadm -D /dev/md0 verifies the devices has a persistent super-block, but 
>> upon reboot, /dev/md0 does not get automatically assembled (an hence is not 
>> a installable/bootable device).
>> 
>> I have created several raid1 arrays and one raid5 array this way and have 
>> never had this problem.  In all fairness, this is the first time I have 
>> used mdadm for the job.  Usually, I boot to something like SysRescueCD, 
>> used raidtools to create my array and then reboot with my Slackware install 
>> CD.
>> 
>> Anyone know why this might be happening? 
>
> Old type arrays are assembled due to having the proper partition type, 0xfd 
> "Linux auto RAID" and are assembled by the kernel. All others are assembled 
> by mdadm running out of initrd or similar, and failures there result from not 
> having a proper config file in the initrd image.
>
> IIRC raidtools does set the array partitions to the auto-assemble partition 
> type. Hope that points you in the right direction. Running
>   "fdisk -l"
> as root will let you see all the partitions, types, etc, for everything on 
> your system.
>
> I may be wrong, I thought auto-assemble only worked with type 0 or 1.
>
> -- 
> bill davidsen <davidsen@tmr.com>
> CTO TMR Associates, Inc
> Doing interesting things with small computers since 1979
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

I use auto-assemble (in conjunction with Debian's own startup scripts) and 
for my root RAID1 device,swap and /boot, it is automatically taken care of 
by the kernel.  For RAID5, it seems to work the same:

[   58.919378] RAID5 conf printout:
[   58.919418]  --- rd:10 wd:10
[   58.919457]  disk 0, o:1, dev:sdc1
[   58.919498]  disk 1, o:1, dev:sdd1
[   58.919539]  disk 2, o:1, dev:sde1
[   58.919579]  disk 3, o:1, dev:sdf1
[   58.919619]  disk 4, o:1, dev:sdg1
[   58.919659]  disk 5, o:1, dev:sdh1
[   58.919719]  disk 6, o:1, dev:sdi1
[   58.919759]  disk 7, o:1, dev:sdj1
[   58.919799]  disk 8, o:1, dev:sdk1
[   58.919839]  disk 9, o:1, dev:sdl1

Justin.

Re: Raid array is not automatically detected.

[Justin Piszcz]

On Sat, 14 Jul 2007, Bill Davidsen wrote:

> Justin Piszcz wrote:
>> 
>> 
>> On Sat, 14 Jul 2007, Bill Davidsen wrote:
>> 
>>> Bryan Christ wrote:
>>>> My apologies if this is not the right place to ask this question. 
>>>> Hopefully it is.
>>>> 
>>>> I created a RAID5 array with:
>>>> 
>>>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 /dev/sdb1 
>>>> /dev/sdc1 /dev/sdd1 /dev/sde1
>>>> 
>>>> mdadm -D /dev/md0 verifies the devices has a persistent super-block, but 
>>>> upon reboot, /dev/md0 does not get automatically assembled (an hence is 
>>>> not a installable/bootable device).
>>>> 
>>>> I have created several raid1 arrays and one raid5 array this way and have 
>>>> never had this problem.  In all fairness, this is the first time I have 
>>>> used mdadm for the job.  Usually, I boot to something like SysRescueCD, 
>>>> used raidtools to create my array and then reboot with my Slackware 
>>>> install CD.
>>>> 
>>>> Anyone know why this might be happening? 
>>> 
>>> Old type arrays are assembled due to having the proper partition type, 
>>> 0xfd "Linux auto RAID" and are assembled by the kernel. All others are 
>>> assembled by mdadm running out of initrd or similar, and failures there 
>>> result from not having a proper config file in the initrd image.
>>> 
>>> IIRC raidtools does set the array partitions to the auto-assemble 
>>> partition type. Hope that points you in the right direction. Running
>>>   "fdisk -l"
>>> as root will let you see all the partitions, types, etc, for everything on 
>>> your system.
>>> 
>>> I may be wrong, I thought auto-assemble only worked with type 0 or 1.
>>> 
>>> -- 
>>> bill davidsen <davidsen@tmr.com>
>>> CTO TMR Associates, Inc
>>> Doing interesting things with small computers since 1979
>>> 
>>> -
>>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>> 
>> 
>> I use auto-assemble (in conjunction with Debian's own startup scripts) and 
>> for my root RAID1 device,swap and /boot, it is automatically taken care of 
>> by the kernel.  For RAID5, it seems to work the same:
>> 
> Are those partitions type "Linux RAID" or is the assemble being run from the 
> init scripts? I suspect the latter.
>> [   58.919378] RAID5 conf printout:
>> [   58.919418]  --- rd:10 wd:10
>> [   58.919457]  disk 0, o:1, dev:sdc1
>> [   58.919498]  disk 1, o:1, dev:sdd1
>> [   58.919539]  disk 2, o:1, dev:sde1
>> [   58.919579]  disk 3, o:1, dev:sdf1
>> [   58.919619]  disk 4, o:1, dev:sdg1
>> [   58.919659]  disk 5, o:1, dev:sdh1
>> [   58.919719]  disk 6, o:1, dev:sdi1
>> [   58.919759]  disk 7, o:1, dev:sdj1
>> [   58.919799]  disk 8, o:1, dev:sdk1
>> [   58.919839]  disk 9, o:1, dev:sdl1
>> 
>> Justin.


The partitions are 0xfd: Auto-detect:

/dev/sdc1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdd1               1       18241   146520801   fd  Linux raid autodetect
/dev/sde1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdf1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdg1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdh1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdi1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdj1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdk1               1       18241   146520801   fd  Linux raid autodetect
/dev/sdl1               1       18241   146520801   fd  Linux raid autodetect

Re: Raid array is not automatically detected.

[Bill Davidsen]

Justin Piszcz wrote:
>
>
> On Sat, 14 Jul 2007, Bill Davidsen wrote:
>
>> Bryan Christ wrote:
>>> My apologies if this is not the right place to ask this question. 
>>> Hopefully it is.
>>>
>>> I created a RAID5 array with:
>>>
>>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 
>>> /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
>>>
>>> mdadm -D /dev/md0 verifies the devices has a persistent super-block, 
>>> but upon reboot, /dev/md0 does not get automatically assembled (an 
>>> hence is not a installable/bootable device).
>>>
>>> I have created several raid1 arrays and one raid5 array this way and 
>>> have never had this problem.  In all fairness, this is the first 
>>> time I have used mdadm for the job.  Usually, I boot to something 
>>> like SysRescueCD, used raidtools to create my array and then reboot 
>>> with my Slackware install CD.
>>>
>>> Anyone know why this might be happening? 
>>
>> Old type arrays are assembled due to having the proper partition 
>> type, 0xfd "Linux auto RAID" and are assembled by the kernel. All 
>> others are assembled by mdadm running out of initrd or similar, and 
>> failures there result from not having a proper config file in the 
>> initrd image.
>>
>> IIRC raidtools does set the array partitions to the auto-assemble 
>> partition type. Hope that points you in the right direction. Running
>>   "fdisk -l"
>> as root will let you see all the partitions, types, etc, for 
>> everything on your system.
>>
>> I may be wrong, I thought auto-assemble only worked with type 0 or 1.
>>
>> -- 
>> bill davidsen <davidsen@tmr.com>
>> CTO TMR Associates, Inc
>> Doing interesting things with small computers since 1979
>>
>> -
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
> I use auto-assemble (in conjunction with Debian's own startup scripts) 
> and for my root RAID1 device,swap and /boot, it is automatically taken 
> care of by the kernel.  For RAID5, it seems to work the same:
>
Are those partitions type "Linux RAID" or is the assemble being run from 
the init scripts? I suspect the latter.
> [   58.919378] RAID5 conf printout:
> [   58.919418]  --- rd:10 wd:10
> [   58.919457]  disk 0, o:1, dev:sdc1
> [   58.919498]  disk 1, o:1, dev:sdd1
> [   58.919539]  disk 2, o:1, dev:sde1
> [   58.919579]  disk 3, o:1, dev:sdf1
> [   58.919619]  disk 4, o:1, dev:sdg1
> [   58.919659]  disk 5, o:1, dev:sdh1
> [   58.919719]  disk 6, o:1, dev:sdi1
> [   58.919759]  disk 7, o:1, dev:sdj1
> [   58.919799]  disk 8, o:1, dev:sdk1
> [   58.919839]  disk 9, o:1, dev:sdl1
>
> Justin.
>


-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: Raid array is not automatically detected.

[Bryan Christ]

I do have the type set to 0xfd.  Others have said that auto-assemble 
only works on RAID 0 and 1, but just as Justin mentioned, I too have 
another box with RAID5 that gets auto assembled by the kernel (also no 
initrd).  I expected the same behavior when I built this array--again 
using mdadm instead of raidtools.

Justin Piszcz wrote:
> 
> 
> On Sat, 14 Jul 2007, Bill Davidsen wrote:
> 
>> Bryan Christ wrote:
>>> My apologies if this is not the right place to ask this question. 
>>> Hopefully it is.
>>>
>>> I created a RAID5 array with:
>>>
>>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda1 
>>> /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
>>>
>>> mdadm -D /dev/md0 verifies the devices has a persistent super-block, 
>>> but upon reboot, /dev/md0 does not get automatically assembled (an 
>>> hence is not a installable/bootable device).
>>>
>>> I have created several raid1 arrays and one raid5 array this way and 
>>> have never had this problem.  In all fairness, this is the first time 
>>> I have used mdadm for the job.  Usually, I boot to something like 
>>> SysRescueCD, used raidtools to create my array and then reboot with 
>>> my Slackware install CD.
>>>
>>> Anyone know why this might be happening? 
>>
>> Old type arrays are assembled due to having the proper partition type, 
>> 0xfd "Linux auto RAID" and are assembled by the kernel. All others are 
>> assembled by mdadm running out of initrd or similar, and failures 
>> there result from not having a proper config file in the initrd image.
>>
>> IIRC raidtools does set the array partitions to the auto-assemble 
>> partition type. Hope that points you in the right direction. Running
>>   "fdisk -l"
>> as root will let you see all the partitions, types, etc, for 
>> everything on your system.
>>
>> I may be wrong, I thought auto-assemble only worked with type 0 or 1.
>>
>> -- 
>> bill davidsen <davidsen@tmr.com>
>> CTO TMR Associates, Inc
>> Doing interesting things with small computers since 1979
>>
>> -
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 
> I use auto-assemble (in conjunction with Debian's own startup scripts) 
> and for my root RAID1 device,swap and /boot, it is automatically taken 
> care of by the kernel.  For RAID5, it seems to work the same:
> 
> [   58.919378] RAID5 conf printout:
> [   58.919418]  --- rd:10 wd:10
> [   58.919457]  disk 0, o:1, dev:sdc1
> [   58.919498]  disk 1, o:1, dev:sdd1
> [   58.919539]  disk 2, o:1, dev:sde1
> [   58.919579]  disk 3, o:1, dev:sdf1
> [   58.919619]  disk 4, o:1, dev:sdg1
> [   58.919659]  disk 5, o:1, dev:sdh1
> [   58.919719]  disk 6, o:1, dev:sdi1
> [   58.919759]  disk 7, o:1, dev:sdj1
> [   58.919799]  disk 8, o:1, dev:sdk1
> [   58.919839]  disk 9, o:1, dev:sdl1
> 
> Justin.

Re: Raid array is not automatically detected.

[David Greaves]

Bryan Christ wrote:
> I do have the type set to 0xfd.  Others have said that auto-assemble 
> only works on RAID 0 and 1, but just as Justin mentioned, I too have 
> another box with RAID5 that gets auto assembled by the kernel (also no 
> initrd).  I expected the same behavior when I built this array--again 
> using mdadm instead of raidtools.

Any md arrays with partition type 0xfd using a 0.9 superblock should be 
auto-assembled by a standard kernel.

If you want to boot from them you must ensure the kernel image is on a partition 
that the bootloader can read - ie RAID 0. This is nothing to do with auto-assembly.

So some questions:
* are the partitions 0xfd ? yes.
* is the kernel standard?
* are the superblocks version 0.9? (mdadm --examine /dev/component)

David

Re: Raid array is not automatically detected.

[dean gaudet]

On Mon, 16 Jul 2007, David Greaves wrote:

> Bryan Christ wrote:
> > I do have the type set to 0xfd.  Others have said that auto-assemble only
> > works on RAID 0 and 1, but just as Justin mentioned, I too have another box
> > with RAID5 that gets auto assembled by the kernel (also no initrd).  I
> > expected the same behavior when I built this array--again using mdadm
> > instead of raidtools.
> 
> Any md arrays with partition type 0xfd using a 0.9 superblock should be
> auto-assembled by a standard kernel.

no... debian (and probably ubuntu) do not build md into the kernel, they 
build it as a module, and the module does not auto-detect 0xfd.  i don't 
know anything about slackware, but i just felt it worth commenting that "a 
standard kernel" is not really descriptive enough.

-dean

Re: Raid array is not automatically detected.

[Justin Piszcz]

On Tue, 17 Jul 2007, dean gaudet wrote:

>
>
> On Mon, 16 Jul 2007, David Greaves wrote:
>
>> Bryan Christ wrote:
>>> I do have the type set to 0xfd.  Others have said that auto-assemble only
>>> works on RAID 0 and 1, but just as Justin mentioned, I too have another box
>>> with RAID5 that gets auto assembled by the kernel (also no initrd).  I
>>> expected the same behavior when I built this array--again using mdadm
>>> instead of raidtools.
>>
>> Any md arrays with partition type 0xfd using a 0.9 superblock should be
>> auto-assembled by a standard kernel.
>
> no... debian (and probably ubuntu) do not build md into the kernel, they
> build it as a module, and the module does not auto-detect 0xfd.  i don't
> know anything about slackware, but i just felt it worth commenting that "a
> standard kernel" is not really descriptive enough.
>
> -dean
>

You're correct-- however, I build out my own kernel.

Justin.

Re: Raid array is not automatically detected.

[David Greaves]

dean gaudet wrote:
> 
> On Mon, 16 Jul 2007, David Greaves wrote:
> 
>> Bryan Christ wrote:
>>> I do have the type set to 0xfd.  Others have said that auto-assemble only
>>> works on RAID 0 and 1, but just as Justin mentioned, I too have another box
>>> with RAID5 that gets auto assembled by the kernel (also no initrd).  I
>>> expected the same behavior when I built this array--again using mdadm
>>> instead of raidtools.
>> Any md arrays with partition type 0xfd using a 0.9 superblock should be
>> auto-assembled by a standard kernel.
> 
> no... debian (and probably ubuntu) do not build md into the kernel, they 
> build it as a module, and the module does not auto-detect 0xfd.  i don't 
> know anything about slackware, but i just felt it worth commenting that "a 
> standard kernel" is not really descriptive enough.

Good point - I should have mentioned the non-module bit!

http://linux-raid.osdl.org/index.php/Autodetect

David

Re: Raid array is not automatically detected.

[Bryan Christ]

I'm now very confused...

When I run mdadm --examine /dev/md0 I get the error message:  No 
superblock detected on /dev/md0

However, when I run mdadm -D /dev/md0 the report clearly states 
"Superblock is persistent"

/dev/md0:
         Version : 00.90.03
   Creation Time : Tue Jul 17 10:17:37 2007
      Raid Level : raid5
      Array Size : 1953535744 (1863.04 GiB 2000.42 GB)
   Used Dev Size : 488383936 (465.76 GiB 500.11 GB)
    Raid Devices : 5
   Total Devices : 5
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Wed Jul 18 10:17:34 2007
           State : clean
  Active Devices : 5
Working Devices : 5
  Failed Devices : 0
   Spare Devices : 0

          Layout : left-symmetric
      Chunk Size : 64K

            UUID : ea6c5a9f:021b4ff8:fc5a08c4:23fc5c4b
          Events : 0.4

     Number   Major   Minor   RaidDevice State
        0       8        1        0      active sync   /dev/sda1
        1       8       17        1      active sync   /dev/sdb1
        2       8       33        2      active sync   /dev/sdc1
        3       8       49        3      active sync   /dev/sdd1
        4       8       65        4      active sync   /dev/sde1

David Greaves wrote:
> Bryan Christ wrote:
>> I do have the type set to 0xfd.  Others have said that auto-assemble 
>> only works on RAID 0 and 1, but just as Justin mentioned, I too have 
>> another box with RAID5 that gets auto assembled by the kernel (also no 
>> initrd).  I expected the same behavior when I built this array--again 
>> using mdadm instead of raidtools.
> 
> Any md arrays with partition type 0xfd using a 0.9 superblock should be 
> auto-assembled by a standard kernel.
> 
> If you want to boot from them you must ensure the kernel image is on a 
> partition that the bootloader can read - ie RAID 0. This is nothing to 
> do with auto-assembly.
> 
> So some questions:
> * are the partitions 0xfd ? yes.
> * is the kernel standard?
> * are the superblocks version 0.9? (mdadm --examine /dev/component)
> 
> David
> 

Re: Raid array is not automatically detected.

[David Greaves]

Bryan Christ wrote:
> I'm now very confused...
It's all that top-posting...


> When I run mdadm --examine /dev/md0 I get the error message:  No 
> superblock detected on /dev/md0
> 
> However, when I run mdadm -D /dev/md0 the report clearly states 
> "Superblock is persistent"

> David Greaves wrote:
>> * are the superblocks version 0.9? (mdadm --examine /dev/component)

See where it says 'component' ? :)

I wish mdadm --detail and --examine were just aliases and the output varied 
according to whether you looked at a component (eg /dev/sda1) or an md device 
(/dev/md0)

I get that wrong *all* the time...

David

Re: Raid array is not automatically detected.

[Bryan Christ]

Ya.  I saw my mistake just a little while ago and running --examine on 
the component worked fine.  I didn't see anything suspicious.

David Greaves wrote:
> Bryan Christ wrote:
>> I'm now very confused...
> It's all that top-posting...
> 
> 
>> When I run mdadm --examine /dev/md0 I get the error message:  No 
>> superblock detected on /dev/md0
>>
>> However, when I run mdadm -D /dev/md0 the report clearly states 
>> "Superblock is persistent"
> 
>> David Greaves wrote:
>>> * are the superblocks version 0.9? (mdadm --examine /dev/component)
> 
> See where it says 'component' ? :)
> 
> I wish mdadm --detail and --examine were just aliases and the output 
> varied according to whether you looked at a component (eg /dev/sda1) or 
> an md device (/dev/md0)
> 
> I get that wrong *all* the time...
> 
> David

Re: Raid array is not automatically detected.

[Bill Davidsen]

David Greaves wrote:
>
> See where it says 'component' ? :)
>
> I wish mdadm --detail and --examine were just aliases and the output 
> varied according to whether you looked at a component (eg /dev/sda1) 
> or an md device (/dev/md0)
>
> I get that wrong *all* the time...

Neil, if you will take that as a suggestion, you can take this as a 
second. While I have learned to use the correct option most of the time, 
this is a case where the software can make an unambiguous decision to 
avoid the human having to stop and think which option is appropriate.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: Raid array is not automatically detected.

[Neil Brown]

On Wednesday July 18, davidsen@tmr.com wrote:
> David Greaves wrote:
> >
> > See where it says 'component' ? :)
> >
> > I wish mdadm --detail and --examine were just aliases and the output 
> > varied according to whether you looked at a component (eg /dev/sda1) 
> > or an md device (/dev/md0)
> >
> > I get that wrong *all* the time...
> 
> Neil, if you will take that as a suggestion, you can take this as a 
> second. While I have learned to use the correct option most of the time, 
> this is a case where the software can make an unambiguous decision to 
> avoid the human having to stop and think which option is appropriate.

The software cannot make an unambiguous decision. It is quite possible
for one md device to be a component of another md device.  In that
case, --examine and --detail are both very meaningful and very
different.

If you have trouble remembering the difference, train yourself to use
--query instead.

I am willing to consider suggestions for improving the error message
when -D or -E don't find what they expect.
I am willing to add aliases that might make it easier to remember the
difference (I confess that I chose 'detail' and 'examine' largely
because they start with 'd' and 'e', to go with assemble, build, and
create)
I am willing to make --query more useful if anyone has any
suggestions.
But I am not willing to make --detail and --examine behave
identically.

NeilBrown

Re: Raid array is not automatically detected.

[Daniel Reichelt]

Hi Bryan,
I was just having the same problem and the mdadm man page clearly states:
----------------------------
--homehost=
    This will override any HOMEHOST setting in the config file and provides the
identity of the host which should be considered the home for any arrays.

    When creating an array, the homehost will be recorded in the superblock.
For version-1 superblocks, it will be prefixed to the array name. For
version-0.90 superblocks, part of the SHA1 hash of the hostname will be stored
in the later half of the UUID.

    When reporting information about an array, any array which is tagged for
the given homehost will be reported as such.

****
    When using Auto-Assemble, only arrays tagged for the given homehost will be
assembled.
****
----------------------------

So just once stop your array and manually assemble it like
mdadm -A <md-device> <components> --homehost=<somestring> --update=homehost
and from the next reboot on, that array, too, will automatically be assembled
by the linux kernel.
HTH
Daniel

Re: Raid array is not automatically detected.

[Bryan Christ]

thanks for the tip!

On Fri, 2008-10-17 at 15:07 +0000, Daniel Reichelt wrote:
> Hi Bryan,
> I was just having the same problem and the mdadm man page clearly states:
> ----------------------------
> --homehost=
>     This will override any HOMEHOST setting in the config file and provides the
> identity of the host which should be considered the home for any arrays.
> 
>     When creating an array, the homehost will be recorded in the superblock.
> For version-1 superblocks, it will be prefixed to the array name. For
> version-0.90 superblocks, part of the SHA1 hash of the hostname will be stored
> in the later half of the UUID.
> 
>     When reporting information about an array, any array which is tagged for
> the given homehost will be reported as such.
> 
> ****
>     When using Auto-Assemble, only arrays tagged for the given homehost will be
> assembled.
> ****
> ----------------------------
> 
> So just once stop your array and manually assemble it like
> mdadm -A <md-device> <components> --homehost=<somestring> --update=homehost
> and from the next reboot on, that array, too, will automatically be assembled
> by the linux kernel.
> HTH
> Daniel