[ML-General] hardware RAID

[david]

On 06/12/15 10:57, Hunter Fuller wrote:
>
> All,
>
> There are a couple of things still to be addressed here...
>
> - David, why did your md raid fail? This should never ever ever ever 
> ever happen. Maybe it didn't fail and the differences you see are in 
> the metadata and boot loader...? I hope that is the case. There's no 
> reason for a md raid 1 to not mirror. If you have that problem, you 
> may have much bigger problems. Such as a failing disk, controller, or 
> something.
>

Hardware was ok.
The system booted, ran everything fine, and worked ok, just not as I 
*wanted.*  When I examined the two drives from a live CD boot, disk 2 
(the actual mirror) was NOTHING like disk 1.  I want identical disks, 
from cylinder 0, track 0, byte 0, all the way to the end of the disk.  
Like I said, immediate fail-over capability, with maybe a boot in 
between if necessary.  mdadm did not do that.  There was an extra 
partition up front on the mirror, no boot partition at all on the 
mirror, and no swap at all.  I was not a happy camper.  Worse, when I 
unplugged the 2nd disk, the first disk would not even boot! Bah.  I 
tried with mdadm on and with it off while trying to boot the first disk 
alone.  (I was going to dd the entire first disk to the second if those 
tests worked but they didn't.)  Absolutely none of the standard disk 
programs would fix it either, so I had to re-init the first disk, and 
lost everything on it because I was so frustrated at the point I didn't 
want to do a full backup.  Turns out, the "mirror" disk would not 
recover no matter what I tried. So, in absolute frustration, I dd'ed 
zero's to the first 3 million bytes of the mirror disk.  Then, I could 
init the 2nd disk and use it as normal, no RAID.  So I am now looking 
into hardware RAID, to see if I can get what I want to happen.  :)

Do you guys know of an intermediate level Linux (or free Winblows) tool 
to show me summaries of the superblock, partitions, and etc, AND allow 
me to adjust them with a little finesse instead of the dd bulldozer?








> - I'm as big of a zfs fanboy as anyone. But remember, you NEED error 
> corrected ram to run zfs! The chances of a
>
>
<<<snip>>>
>
>     Oh and with ZFS you can use different size drives but you waist a
>     good amount of space when you do that.
>     And lastly be sure to schedule scrubs of your drives and do it in
>     a way that the scrub will not occur while a long smart test is
>     running.  That can cause problems.
>
> Can I ask what type of problems?
>
>     According to the forums.  "It isnt able to handle a scrub, offline
>     test and normal traffic well."
>     https://forums.freenas.org/index.php?threads/scrub-and-smart-testing-schedules.20108/
>
>     Sounds like performance.  The guy who made the post (cyberjock) is
>     one of their forum admins and he has helped me with some difficult
>     questions so I trust his opinion.
>
>             -Kirk
>
>

Seems like it would be very unwise to run scrub and s.m.a.r.t. tests on 
a live disk!  That would have to be one very intelligent controller, 
probably with a very large cache.




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