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Re: 128TB filesystem limit?

To: david@xxxxxxx
Subject: Re: 128TB filesystem limit?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 26 Mar 2010 11:35:11 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <alpine.DEB.2.00.1003251702190.12435@xxxxxxxxxxxxxx>
References: <alpine.DEB.2.00.1003251609160.12435@xxxxxxxxxxxxxx> <20100325235433.GM3335@dastard> <alpine.DEB.2.00.1003251702190.12435@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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....

> >>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

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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