RE: What to do about df and btrfs fi df

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Any plans on having "brtfs fi df" report more precise values rather then rounded off to the nearest hundredth of a unit. full kilobytes(1024 bytes =1Kib) or in bytes would be nice

Current output:

# btrfs fi df /data
Data, single: total=1.37TiB, used=1.35TiB
System, DUP: total=8.00MiB, used=192.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, DUP: total=3.00GiB, used=1.62GiB
Metadata, single: total=8.00MiB, used=0.00

Better would be:

# btrfs fi df /data
Data, single: total=14123412341 bytes, used=1342343 bytes
...etc you know what I mean...

I wish there was more you know.

Kind Regards,

Kostia

 Consider the environment. Please don't print this e-mail unless you really need to.

-----Original Message-----
From: linux-btrfs-owner@xxxxxxxxxxxxxxx [mailto:linux-btrfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Sandy McArthur
Sent: Tuesday, February 11, 2014 12:54 PM
To: linux-btrfs@xxxxxxxxxxxxxxx
Cc: Josef Bacik
Subject: Re: What to do about df and btrfs fi df

Maybe this is too much of a break from tradition but I think df should report the min(device free space, remaining quota) for the particular volume being queried.


On Mon, Feb 10, 2014 at 11:41 AM, Josef Bacik <jbacik@xxxxxx> wrote:
> Hello,
>
> So first of all this is going to get a lot of responses, so straight 
> away I'm only going to consider your opinion if I recognize your name 
> and think you are a sane person.  This basically means any big 
> contributors and we'll make sanity exceptions for cwillu.
>
> These are just broad strokes, let us not get bogged down in the 
> details, I just want to come to a consensus on how things _generally_ 
> should be portrayed to the user.  We can worry about implementation 
> details once we agree on the direction we want to go.
>
> We all know space is a loaded question with btrfs, so I'm just going 
> to explain the reasoning of why we chose what we chose originally and 
> then offer the direction we should go in.  If you agree say yay, if 
> not please provide a very concise alternative suggestion with a very 
> short explanation of why it is better than I'm suggesting.  I'm not 
> looking to spend a whole lot of time this problem.
>
> Also this isn't going to address b_avail, cause frankly that is some 
> fucking voodoo right there, suffice it to say we will just adjust 
> b_avail based on how we should represent total and used.
>
> ===== ye olde df =====
>
> I don't remember what we did originally, but IIRC we would only show 
> used space from the block groups and would show the entire size of the 
> fs.  So for example with two 1 tb drives in RAID1 you'd see ENOSPC and 
> look at df and it would show total of 2TB and used at 1TB.  Obviously 
> not good, so we switched to the mechanism we have today, which is you 
> see 2TB for total, you see 2TB for used and you see 0 for available.  
> We just scaled up the used and available based on your raid multiplier.
>
> ===== btrfs fi df =====
>
> I made this for me because of ENOSPC issues but of course it's also 
> really useful for users.  It is just a dump of the block group 
> information and their flags, so really just spits out bytes_used and total_bytes and flags.
> Because at the block_group/space_info level in btrfs we don't care 
> about how much actual space is taken up this number is not adjusted 
> for RAID values, and these numbers are reflected in the tools output.  
> So if you have RAID1 you need to mentally multiply the Total and Used 
> values by 2 because that is how much actual space is being used.
>
> =====  What to do moving forward =====
>
> Flip what both of these do.  Do not multiply for normal df, and 
> multiply for btrfs fi df.
>
> ===== New and improved df =====
>
> Since this is the lowest common denominator we should just spit out 
> how much space is used based on the block groups and then divide the 
> remaining space that hasn't been allocated yet by the raid multiplier.
>
> This is going to be kind of tricky once we do per-subvolume RAID 
> levels, but this falls under the b_avail voodoo which is just a guess 
> anyway, so for this we will probably take the biggest multiplier and 
> use that to show how much available space you have.
>
> This way with RAID1 it shows you have 1tb of total space and you've 
> used 1tb of space.
>
> ===== New and improved btrfs fi df =====
>
> Since people using this tool are already going to be better informed 
> and since we are already given the block group flags we can go ahead 
> and do the raid multiplier in btrfs-progs and spit out the adjusted 
> numbers rather than the raw numbers we get from the ioctl.  This will 
> just be a progs thing and that way we can possibly add an option to 
> not apply the multipliers and just get the raw output.
>
> ===== Conclusion =====
>
> Let me know if this is acceptable to everybody.  Remember this is just 
> broad strokes, keep your responses short and simple or I simply won't read them.
> Thanks,
>
> Josef
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--
Sandy McArthur

"He who dares not offend cannot be honest."
- Thomas Paine
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