[ML-General] hardware RAID

[Hunter Fuller]

Unfortunately there is no RAID (that I am aware of) that will give you
a 100% identical disk. Every RAID I have seen has required a header to
be present on the disk so that it can be recognized if it is moved
around. I know this applies to Intel, LSI, and md raid.
--
Hunter Fuller




On Fri, Jun 12, 2015 at 11:13 AM, david <ainut at knology.net> wrote:
>
>
> 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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