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Re: Maximum file system size of XFS?

To: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Subject: Re: Maximum file system size of XFS?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 12 Mar 2013 09:19:36 +1100
Cc: xfs@xxxxxxxxxxx, Pascal <pa5ca1@xxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <201303112257.00798.Martin@xxxxxxxxxxxx>
References: <20130309215121.0e614ef8@thinky> <201303112245.40522.Martin@xxxxxxxxxxxx> <201303112257.00798.Martin@xxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Mar 11, 2013 at 10:57:00PM +0100, Martin Steigerwald wrote:
> Am Montag, 11. März 2013 schrieb Martin Steigerwald:
> > 2) Create a insanely big sparse file
> > 
> > merkaba:~> truncate -s1E /mnt/zeit/evenmorecrazy.img
> > merkaba:~> ls -lh /mnt/zeit/evenmorecrazy.img
> > -rw-r--r-- 1 root root 1,0E Mär 11 22:37 /mnt/zeit/evenmorecrazy.img
> > 
> > (No, this won´t work with Ext4.)
> Okay, you can´t go beyond 8 EiB for a single file which is about what I have 
> read somewhere:

Right - file size offsets max out at 2^63 bytes.


> merkaba:/mnt/zeit#5> vgcreate --physicalextentsize 4G  justinsane /dev/loop0 
> /dev/loop1
>   Volume group "justinsane" successfully created
> merkaba:/mnt/zeit> vgs                                                        
>   VG         #PV #LV #SN Attr   VSize   VFree 
>   justinsane   2   0   0 wz--n-  14,00e 14,00e
>   merkaba      1   4   0 wz--n- 278,99g  4,85g
> merkaba:/mnt/zeit>
> Enough insanity for today :)
> I won´t mkfs.xfs on it, the 20 GiB of the just filesystem wouldn´t be 
> enough.

Right - I did a mkfs.xfs on a (8EB - 1GB) file a couple of days ago
just to check it worked. I killed it after a short while, because I
didn't feel like needlessly subjecting the SSDs the file was
physically located on to the 25 million sparse sector sized writes
needed for mkfs to complete.

And you can double that number of writes needed for a 16EB
filesystem to be initialised by mkfs. So, theory be damned, even
mkfs.xfs doesn't scale to supporting exabyte filesystems...


Dave Chinner

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