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Re: 128TB filesystem limit?

To: xfs@xxxxxxxxxxx
Subject: Re: 128TB filesystem limit?
From: Steve Costaras <stevecs@xxxxxxxxxx>
Date: Fri, 26 Mar 2010 02:26:28 -0500
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On 03/25/2010 23:56, david@xxxxxxx wrote:
On Thu, 25 Mar 2010, Eric Sandeen wrote:

david@xxxxxxx wrote:
On Fri, 26 Mar 2010, Dave Chinner wrote:

...

Is there any reason for putting partitions on these block devices?
You could just use the block devices without partitions, and that
will avoid alignment potential problems....

I would like to raid to auto-assemble and I can't do that without
partitions, can I

I think you can.... it's not like MD is putting anything in the partition
table; you just give it block devices, I doubt it cares if it's a whole
disk or some partition.

Worth a check anyway ;)

I know that md will work on raw devices, but the auto-assembly stuff looks for the right partition type, I would have to maintain a conf file across potential system rebuilds if I used the raw partitions.

...


the next fun thing is figuring out what sort of stride, etc parameters I
should have used for this filesystem.

mkfs.xfs should suss that out for you automatically based on talking to md;
of course you'd want to configure md to line up well with the hardware
alignment.

in this case md thinks it's working with 10 12.8TB drives, I really doubt that it's going to do the right thing.

I'm not exactly sure what the right thing is in this case. the hardware raid is useing 64K chunks across 16 drives (so 14 * 64K worth of data per stripe), but there are 10 of these stripes before you get back to hitting the same drive again.

David Lang


It does here at least, I never use partition tables on any of the arrays here just use LVM against what it sees as the 'raw' disk. I haven't tried it w/ a 128TB array but with smaller ones that's what I've used in the past (hw raid, md raid-0, file system). Recently for systems now I just use HW raid; LVM; and then filesystem (lvm does the striping/raid-0 function). when you create the physical volume w/ lvm just make sure you allign it (older versions use --metadatasize to 'pad' the start offset), newer versions have the dataalignment option.


Steve

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