Re: Questions about RAID 6
Hi
I recently (last week), migrated from 10 x 1Tb to adaptec 51645 and 5
x 2T drives.
my experience, I can't get frub2 and the adaptec to work, so I am
booting from a SSD I had.
I carved up the 5x2T into 32G (mirror 1e - mirror stripe + parity) -
too boot from and mirrored against my ssd. the rest went into a raid5
till i moved my info over - this took around 18 hours, my data was
originally on a vgs on a pv on my raid6 mdadm I made the adaptec 5T
into a pv and added it to the vg and then did a pvmove - that took
time :)
next I went and got 2 more 2Tb drives and did an online upgrade from
5x2T raid5 to 7x2Tb raid6 now sitting at 9T - this took about 1 week
to resettle.
Other quirks I had to used parted to install gpt partition table on
the drive it was over some limit for mbr's. Had a bit of a scare when
I resized my pvs partition with parted, it submits each command once
its typed - I had to delete my pv partition and then recreate it -
same as deleting a partition and then recreating it, but with fdisk it
doesn't really happen until Write time.... 5 T of info gone
potentially .... could not use the resize command it did not under
stand lvm/pv's
But all is okay now resized and ready.
I choose raid6 because its just another drive and I value my data more
than another drive. I also have 3 x 1T in the box in the raid 1ee
setup which is stripe / mirror / parity setup.
I don't use batter backup to the machine, I have a ups attached, which
can run it for 40 min on battery.
Note - I also backup all my data to another server close by but
another bulding and all the important stuff get backed up off site. I
use rdiff-backup
Alex
On Tue, Apr 27, 2010 at 2:11 PM, Tim Clewlow <tim@clewlow.org> wrote:
>
>> I don't know what your requirements / levels of paranoia are, but
>> RAID 5 is
>> probably better than RAID 6 until you are up to 6 or 7 drives; the
>> chance of a
>> double failure in a 5 (or less) drive array is minuscule.
>>
> .
> I currently have 3 TB of data with another 1TB on its way fairly
> soon, so 4 drives will become 5 quite soon. Also, I have read that a
> common rating of drive failure is an unrecoverable read rate of 1
> bit in 10^14 - that is 1 bit in every 10TB. While doing a rebuild
> across 4 or 5 drives that would mean it is likely to hit an
> unrecoverable read. With RAID 5 (no redundancy during rebuild due to
> failed drive) that would be game over. Is this correct?
>
> Tim.
>
>
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