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Re: 128TB filesystem limit?

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: 128TB filesystem limit?
From: david@xxxxxxx
Date: Thu, 25 Mar 2010 19:02:31 -0700 (PDT)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100326003511.GN3335@dastard>
References: <alpine.DEB.2.00.1003251609160.12435@xxxxxxxxxxxxxx> <20100325235433.GM3335@dastard> <alpine.DEB.2.00.1003251702190.12435@xxxxxxxxxxxxxx> <20100326003511.GN3335@dastard>
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)
On Fri, 26 Mar 2010, Dave Chinner wrote:

On Thu, Mar 25, 2010 at 05:03:52PM -0700, david@xxxxxxx wrote:
On Fri, 26 Mar 2010, Dave Chinner wrote:

On Thu, Mar 25, 2010 at 04:15:42PM -0700, david@xxxxxxx wrote:
I'm working with a raid 0 (md) array on top of 10 16x1TB raid 6
hardware arrays.
....
I then did mkfs.xfs /dev/md0

but a df is showing me 128TB

What is in /proc/partitions?

# cat /proc/partitions
major minor  #blocks  name

   8        0  292542464 sda
   8        1    2048287 sda1
   8        2    2048287 sda2
   8        3    2048287 sda3
   8        4  286390755 sda4
   8       16 13671874048 sdb
   8       17 13671874014 sdb1
   8       32 13671874048 sdc
   8       33 13671874014 sdc1
....
   8      160 13671874048 sdk
   8      161 13671874014 sdk1
   9        0 136718739840 md0

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

is this just rounding error combined with the 1000=1k vs 1024=1k
marketing stuff,

Probably.

or is there some limit I am bumping into here.

Unlikely to be an XFS limit - I was doing some "what happens if"
testing on multi-PB sized XFS filesystems hosted on sparse files
a couple of days ago....

Ok, 128TB is a suspiciously round (in computer terms) number,
especially when the math is 10 sets of 14 drives (each 1TB), so I
figured I'd double check.

136718739840 / 10^9 = 136.72TB    <==== marketing number
136718739840 / 2^30 = 127.33TiB   <==== what df shows

Thanks.

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

David Lang

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