6

What should I do to determine chuck size of existing raid arrays. I'm using software raid created by mdadm.

I've been probing around for a while and can't find the right utility to that job.

mdadm --detail /dev/md/0

mdadm --examine /dev/sda0

and

cat /proc/mdstat

doesn't say any thing about chunk size.

cat /sys/block/md0/md/chunk_size

returns 0

Improve this question

1 Answer 1

Reset to default
5

Looks like you can run

mdadm -E /dev/sda1

or similar against one of the devices in the array. It will print the superblock and lists the chunk size there. Note that the switch is -E, not -e.

See the third grey section here

EDIT: See here and here on chunk size in RAID1

Improve this answer
5
  • thanx for replying. i forgot to mention that i did call --examine on the device and nothing was printed about chunk-size. here's an example output. is it my mdadm version (v3.1.4) or metadata version that makes the difference?
    – Huang Tao
    Commented Aug 30, 2011 at 8:38
  • 1
    I've seen two thoughts on this. One, since RAID 1 doesn't stripe, chunk size is irrelevant. In another, it's only relevant to reads/seeks. My guess is, it wasn't set since it's RAID one, and if it has a value, it's the default 64k
    – OldWolf
    Commented Aug 31, 2011 at 16:03
  • Your output says you're using RAID1. See the comment and two links I've added above.
    – OldWolf
    Commented Aug 31, 2011 at 16:13
  • 3
    i'm aware that i was using the 64k default chunk-size. i've read the man pages and the wikipedia article before i asked the question. however, since "the chunk-size specifies how much data to read serially from the participating disks", it does matter for raid 1 arrays, doesn't it? i mean, it's supposed to take chunk-size into consideration tuning the filesystem lying on the array, right?
    – Huang Tao
    Commented Aug 31, 2011 at 17:05
  • You'd probably want the chunk size to be small enough so that application requests get distributed over drives and big enough to not spend a lot of time splitting or assembling data streams.For SSDs, it's get a bit more complicated as the internal erase block size of the drive will impact performance. A chunk size of 1 MiB or more can be a good choice.
    – Joachim Wagner
    Commented May 12 at 12:19

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .