CentOS - Feb 2015 - OT: AF 4k sector drives with 512 emulation

Chris Murphy wrote:
<snip>
> The emulation implementations don't come into play if the alignment is
> correct from the start. The better implementations have significantly
> less pathological behavior if alignment is wrong, but that's
> anecdotal, I don't have any empirical data available. But I'd say
in
> any case you want it properly aligned.
You really, really want it properly aligned. We ran into that problem when
we started getting 3TB drives a couple-three years ago. Proper alignment
made a measured... trying to remember, but I think it was at *least* 20%
difference in throughput.

Alignment's easy: using parted (the user-hostile program), if you do go in
with parted -a optimal /dev/drive, and do
mkpart pri ext4 0.0GB 100% (for non-root drives, for example), it's
aligned correctly.

        mark

On 2/27/2015 3:06 PM, m.roth at 5-cent.us wrote:
> Alignment's easy: using parted (the user-hostile program), if you do go
in
> with parted -a optimal /dev/drive, and do
> mkpart pri ext4 0.0GB 100% (for non-root drives, for example), it's
> aligned correctly.
i found -a optimal to do weird things, and almost always complain.    I 
just use -a none now, and specify partition start in (512b) sectors, like..

     # parted /dev/sdc
     align none
     mklabel gpt
     mkpart pri 512s -1s

don't start at 0, as thats where the MBR or GPT has to go.    512 
sectors is 256K bytes, which puts you on a erase block boundary with 
most SSD's as well as HD's.    -1s is end of the disk.



-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast

The default for fdisk, parted, and gdisk is starting the first
partition on LBA 2048, which is 8 sector aligned. You don't need any
options. The alternative is to simply not partition the drives or the
resulting RAID and just format it.

Chris Murphy