[CentOS] Booting Software RAID

m.roth at 5-cent.us m.roth at 5-cent.us
Tue Jan 28 22:47:21 UTC 2014


John R Pierce wrote:
> On 1/28/2014 1:35 PM, Leon Fauster wrote:
>>> >As I noted in a previous post, it's got to be GPT, not MBR - the
>>> latter
>>> >doesn't understand > 2TB, and won't.
>> IMHO this applies only to partitions (eg. 3TB HD with MBR 1x1TB, 1x2TB
>> Partition).
>
> it also applies to 3TB drive with 3TB partition, such as you typically
> use with LVM.
>
> I don't like using raw disk devices in most cases as they aren't labeled
> so its impossible to figure out whats on them at some later date.
>
> just use the gpt partitioning tools and you'll be fine.   as long as its
> not the boot device, the BIOS doesn't even need to know about GPT.
>
> |parted /dev/sdb ||"mklabel gpt"|
> |parted -a none /dev/sdb ||"mkpart primary 512s -1s"
>
> that creates a single /dev/sdb1 partition using the whole drive starting
> at the 256kB boundary (which should be a nice round place on most raid,
> SSD, etc... the defaults are awful, the start sector is at an odd
> location)

Not a fan of that - a lot of the new drives actually use 4k blocks, *not*
512b, but serve it logically as 512. HOWEVER, you can see a real
performance hit. my usual routine is
parted -a optimal
mklabel gpt
mkpart pri ext4 0.0GB 3001.0GB
q
and that aligns them for optimal speed. The 0.0GB will start at 1M - the
old start at sector(?) 63 will result in non-optimal alignment, not
starting on a cylinder boundry, or something. Note also that parted is
user hostile, so you have to know the exact magical incantations, or you
get "this is not aligned optimally", but no idea of what it thinks you
should do. What I did, above, works.

        mark




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