On Mon, Nov 15, 2010 at 08:52:32AM +0200, Zoltan Szecsei wrote:
On 2010-11-14 21:50, Luca Berra wrote:
On Sun, Nov 14, 2010 at 05:36:38PM +0200, Zoltan Szecsei wrote:
*Partition alignment?
Is this relevant for modern HDs (I'm using 5900rpm Seagate 2TB drives)
for modern hdds with 4k sectors it is
new fdisk and/or parted should already know how to align
fdisk reports 512b sectors:
root@gs0:/home/geograph# fdisk -lu
i believe your fdisk does not support getting geometry from blkid, but i
am not an ubuntu user
you could try checking with something like 'strings /sbin/fdisk | grep io_size',
but since we are going without partitions you can ignore all this.
btw to check sector size on a disk, on a fairly recent kernel you can
check the files under /sys/block/*/queue,
hw_sector_size
minimum_io_size
optimal_io_size
except for disks that lie about their sector size, but this is a
different story.
*After partitioning the 8 drives, is this the correct sequence?
mdadm --create /dev/md0 --metadata=1.2 --auto=md --chunk=64 --level=raid6
why you state the chunk size here, i tought you wanted to stay with the
defauklt
because on my mdadm, 64 is the default - and I was just re-enforcing that
for the reader.
root@gs0:/home/geograph# mdadm -V
mdadm - v2.6.7.1 - 15th October 2008
this mdadm release is a tad old (about two years), it will work, but
some things may be different than current 3.1.x
root@gs0:/home/geograph#
*After this, do I mkfs ext4 first, or LVM first?
if you want to use lvm it would be lvm first, but... do you want to?
there is no point if the aim is allocating the whole space to a single
filesystem.
Because I might want to join this array to another one at a later stage - I
would then have 2 boxes each with 8 drives, and each with a SiI3132 card on
the same motherboard.
I might use the second box to mirror the first, or to extend it - not sure
of my needs yet.
ok, then you need to align lvm as well
check if you have these parameters in /etc/lvm/lvm.conf
md_chunk_alignment = 1
data_alignment_detection = 1
if you don't have those at all, check if lvm supports them
strings /sbin/lvm|grep io_size
if not, you have to align manually, using the --dataalignment option to
pvcreate, align to a full stripe (chunk_size * 6, see below)
*What stride and stripe values should I use?
stride=chunk_size/fs block size
stripe-width=stride * num_data_disks
num_data disks in your case is 6, 8 total disks - 2 parity disks
on a fairly recent kernel:
/sys/block/md?/queue/minimum_io_size would be the chunk_size of the array
/sys/block/md?/queue/optimal_io_size would be the stripe size
this should be exported on lvm devices also
/sys/block/dm-*/queue/...
so you can check with data in /sys/block at each step which is the value
to feed into tools.
new toolstack should already find the correct stripe/stride for you
How would I check ?
strings /sbin/lvm|grep io_size
--
Luca Berra -- bluca@xxxxxxxxxx
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