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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 17:03:52 -0700 (PDT)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100325235433.GM3335@dastard>
References: <alpine.DEB.2.00.1003251609160.12435@xxxxxxxxxxxxxx> <20100325235433.GM3335@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 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.

fdisk -l shows me 10 drives like

WARNING: GPT (GUID Partition Table) detected on '/dev/sdk'! The util
fdisk doesn't support GPT. Use GNU Parted.


Disk /dev/sdk: 13999.9 GB, 13999999025152 bytes
255 heads, 63 sectors/track, 1702069 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdk1               1      267350  2147483647+  ee  EFI GPT

and then the md0 device as

Disk /dev/md0: 139999.9 GB, 139999989596160 bytes
2 heads, 4 sectors/track, -1 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table


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       48 13671874048 sdd
   8       49 13671874014 sdd1
   8       64 13671874048 sde
   8       65 13671874014 sde1
   8       80 13671874048 sdf
   8       81 13671874014 sdf1
   8       96 13671874048 sdg
   8       97 13671874014 sdg1
   8      112 13671874048 sdh
   8      113 13671874014 sdh1
   8      128 13671874048 sdi
   8      129 13671874014 sdi1
   8      144 13671874048 sdj
   8      145 13671874014 sdj1
   8      160 13671874048 sdk
   8      161 13671874014 sdk1
   9        0 136718739840 md0

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.

David Lang

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