I travelled twice in the past !!

["Edouard Gaulué" <edouard.gaulue@ensg.ign.fr>]

Dear all,

I'm sory I didn't get the time to read the whole list and my Internet 
researchs kept sending me to linux soft-raid howtos. So I send a mail to 
this list.

This is the second time I travelled in the past due to my linux soft 
RAID 1 system (mis)configuration.

Here is what I can say :
- I've got plenty of production servers configured in RAID 1 using the 
2.4.24 debian patched linux kernel.
- I often go on those machines and a cat /proc/mstat seems to report me 
that disks are synchronized. Should I trust this kind of information ?
- Those machines often turn more than a year long without being reboot.
- Sometime due to hardware problems, or a need for a kernel change I 
have to reboot them.
- Sometime this reboot fail.
- This morning, it failled and I needed to use a Knoppix CD to get back 
to my system, chroot, repair the problem and reboot.
- I needed to assemble my array before to mount it, what I did with : 
mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1.
- The system answered it had to resynchronize the disks.
- After this, the data I got were about one year ago...

My opinion and questions :
- I thought that in RAID 1, writes were made on the 2 disks and reads 
half/half on the first and the second. Am I wrong ?
- I've got the feeling that starting a certain day  (don't know which 
one), it stopped behave this way. Is this happening often ? Is it a bug 
? How to detect this behaviour ?
- When I re-assembled the disk : no luck, it resynchronized the older 
with the knew one, so I get in the past.

Please help me, telling me if it's a misunderstanding on the way RAID 1 
should work, if I had to make more control with special tools, if it's a 
bug, if it depends on the kernel version...

EG

-- 
========================================================================
Édouard GAULUÉ
ENSG - IGN                             Réseau et Systèmes Informatiques
6-8 avenue Blaise Pascal               Activité IGS & DORIS
F-77455 MARNE LA VALLEE CEDEX 2        Master MSIAG
Tel : +33 (0) 1 64 15 32 43
Mail : Edouard.Gaulue@ensg.ign.fr

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