[linux-lvm] I'm confused

[linux-lvm] I'm confused

[David Corbin]

Hopefully, the following "summary" will make sense.
---start---
piano:/data/family# 
vgscan                                                                                                               
vgscan -- reading all physical volumes (this may take a 
while...)                                                                        
vgscan -- found active volume group 
"vg0"                                                                                                
vgscan -- "/etc/lvmtab" and "/etc/lvmtab.d" successfully created
vgscan -- WARNING: This program does not do a VGDA backup of your volume 
group

piano:/data/family# vgdisplay
--- Volume group ---
VG Name               vg0
VG Access             read/write
VG Status             available/resizable
VG #                  0
MAX LV                256
Cur LV                1
Open LV               1
MAX LV Size           255.99 GB
Max PV                256
Cur PV                1
Act PV                1
VG Size               109.77 GB
PE Size               4 MB
Total PE              28102
Alloc PE / Size       109 / 436 MB
Free  PE / Size       27993 / 109.35 GB
VG UUID               hC86w2-zjFf-x2gt-1GC4-LHET-6ieO-BiC5j5


piano:/data/family# lvscan
lvscan -- ACTIVE            "/dev/vg0/data" [436 MB]
lvscan -- 1 logical volumes with 436 MB total in 1 volume group
lvscan -- 1 active logical volumes

piano:/data/family# df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/hda2              1921188    672176   1151420  37% /
/dev/hda1                23302      4905     17194  23% /boot
/dev/vg0/data           446444    444448      1996 100% /data
piano:/data/family#
---end---

I'm having trouble reconciling the 436MB   of the "df" with the VG Size 
of vgdisplay.  Obviously something is wrong somewhere.  I KNOW I'm no 
where near using up my 120G drive yet.

For the record, this is a Debian Woody system running a 2.4.19 kernel.

Help.

Thanks
David Corbin

Re: [linux-lvm] I'm confused

[Cameron Hutchison]

Once upon a time David Corbin said...
>
> I'm having trouble reconciling the 436MB   of the "df" with the VG Size 
> of vgdisplay.  Obviously something is wrong somewhere.  I KNOW I'm no 
> where near using up my 120G drive yet.

Nothing is wrong. Generally you can't directly reconcile the output of
df with the VG size. df output correlates to LV sizes.

Here's what you've got:

> VG Size               109.77 GB

Your volume group (vg0) is about 110GB (I gather the other 10GB of your
drive is allocated to other partitions).

> Alloc PE / Size       109 / 436 MB

You've used up (allocated) 436MB of the volume group

> Free  PE / Size       27993 / 109.35 GB

You have still almost 110GB free (since you allocated only 436MB)

> lvscan -- ACTIVE            "/dev/vg0/data" [436 MB]

Your data partition is the only LV and that is using the 436MB used in
vg0.

> /dev/vg0/data           446444    444448      1996 100% /data

Your filesystem on /dev/vg0/data is using the entire 436MB of the
partition. And its full.


What you need to do now is extend your logical volume to allocate more
space to it. Then resize the filesystem. If you have an ext2/ext3
filesystem, you use "e2fsadm --size ...". If you have xfs, you use
"xfs_growfs ...". I dont know about other filesystem types.

eg. to add 10G to your data partition (assuming xfs - that's what I use):
# lvextend --size +10G /dev/vg0/data
# xfs_growfs /dev/vg0/data

df(1) should now show a large filesystem with much more space.

Re: [linux-lvm] I'm confused

[David Corbin]

>
>
>>VG Size               109.77 GB
>>    
>>
>
>Your volume group (vg0) is about 110GB (I gather the other 10GB of your
>drive is allocated to other partitions).
>  
>
Well, About 3 gig is other partions, and it appears to me that the other 
7G is lost to making the raid device and various overheads (though that 
sure seems excessive).

>  
>
>>Alloc PE / Size       109 / 436 MB
>>    
>>
>
>You've used up (allocated) 436MB of the volume group
>
>  
>
>>Free  PE / Size       27993 / 109.35 GB
>>    
>>
>
>You have still almost 110GB free (since you allocated only 436MB)
>
>  
>
>>lvscan -- ACTIVE            "/dev/vg0/data" [436 MB]
>>    
>>
>
>Your data partition is the only LV and that is using the 436MB used in
>vg0.
>
>  
>
>>/dev/vg0/data           446444    444448      1996 100% /data
>>    
>>
>
>Your filesystem on /dev/vg0/data is using the entire 436MB of the
>partition. And its full.
>
>  
>
The odd thing is that I'm sure I created the LV at a full 100% of the 
disk...

>What you need to do now is extend your logical volume to allocate more
>space to it. Then resize the filesystem. If you have an ext2/ext3
>filesystem, you use "e2fsadm --size ...". If you have xfs, you use
>"xfs_growfs ...". I dont know about other filesystem types.
>
>eg. to add 10G to your data partition (assuming xfs - that's what I use):
># lvextend --size +10G /dev/vg0/data
># xfs_growfs /dev/vg0/data
>
>df(1) should now show a large filesystem with much more space.
>  
>
I did as you suggested, and used "resize_reiserfs".  It seems better, 
but we shall see if it changes on me again...

Re: [linux-lvm] I'm confused

[Pantaleimon]

On Sunday 08 December 2002 12:25, David Corbin wrote:

[snip]

> Well, About 3 gig is other partions, and it appears to me that the other
> 7G is lost to making the raid device and various overheads (though that
> sure seems excessive).
>

I think hardisk manufacturers use base 10, rather than base 2, when they speak 
of "mega" and "giga", ie. mega = 1000K and not 1024K. That means that a 120G 
hardisk is only 114.4G. Hence, 109.77G + about 3G = about 113G. Hmm, still 
about 1.5G missing.

Re: [linux-lvm] I'm confused

[Steven Lembark]

-- Pantaleimon <pantaleimon@home.no>

> On Sunday 08 December 2002 12:25, David Corbin wrote:
>
> [snip]
>
>> Well, About 3 gig is other partions, and it appears to me that the other
>> 7G is lost to making the raid device and various overheads (though that
>> sure seems excessive).
>>
>
> I think hardisk manufacturers use base 10, rather than base 2, when they
> speak  of "mega" and "giga", ie. mega = 1000K and not 1024K. That means
> that a 120G  hardisk is only 114.4G. Hence, 109.77G + about 3G = about
> 113G. Hmm, still  about 1.5G missing.

They also quote the size before laying down timing tracks
and bad block mappings -- along with the bad blocks. That
accounts for another 10%.

Drives look kind of like modern lumber: you have to ignore
the nominal size in your calculations and deal with finished
size in order to plan for anything -- or just accept that
10% "shrinkage" is a normal part of life.


--
Steven Lembark                               2930 W. Palmer
Workhorse Computing                       Chicago, IL 60647
                                            +1 800 762 1582

Re: [linux-lvm] I'm confused

[William Blunn]

> > I think hardisk manufacturers use base 10, rather than base 2, when they
> > speak  of "mega" and "giga", ie. mega = 1000K and not 1024K. That means
> > that a 120G  hardisk is only 114.4G. Hence, 109.77G + about 3G = about
> > 113G. Hmm, still  about 1.5G missing.
> 
> They also quote the size before laying down timing tracks
> and bad block mappings -- along with the bad blocks. That
> accounts for another 10%.

What you are saying is completely wrong.

When a drive manufacturer quotes a drive with a capacity of 100 GB, what
they are quoting is the *user* capacity.

There are at least 100 GB available to the "user".

The "user" is the host machine.

For a typical 512 byte block size that will mean that there will be at
least:

   100 x 10^9 / 512 blocks

   195 312 500 blocks

available to the *user*, i.e. the host machine.

Whatever the drive uses internally is not counted.

If you look at drive specs, you will sometimes see a figure quoted for
"user data sectors" (in this case 195 312 500) and this always indicates
a capacity higher than the quoted drive capacity.

Bill
-- 
William H. Blunn - <bill+s.9sfuw6uo@tao-group.com> - Developer Support
Tao
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Re: [linux-lvm] I'm confused

[William Blunn]

> I think hardisk manufacturers use base 10, rather than base 2,
> when they speak of "mega" and "giga", ie. mega = 1000K and not
> 1024K. That means that a 120G hardisk is only 114.4G.

No.

You are right in that "mega = 1000K", but from your figure of 114.4, you
still appear to have "K = 1024" and "G = 1024M", both of which are
wrong.

Hard disk manufacturers use SI defined multipliers, i.e. they use a
documented standard.

  K = 10^3
  M = 10^6
  G = 10^9

  120 GB = 120 000 000 000 B

Computer people have traditionally abused these symbols to mean
multipliers with similar values, but based on powers of two.

Symbols have been defined for these multipliers, but some people still
haven't caught up to them.

  Ki = 2^10 = 1024
  Mi = 2^20 = 1048576
  Gi = 2^30 = 1073741824

So

  120 GB ~= 111.8 GiB

Interestingly, LVM1's vgdisplay incorrectly uses "GB" in its output
where it should say "GiB".

Bill
-- 
William H. Blunn - <bill+s.9sfuw6uo@tao-group.com> - Developer Support
Tao
62/63 Suttons Business Park, Earley, READING, RG6 1AZ, United Kingdom
Tel: +44 118 901 2999 - Fax: +44 118 901 2963 - http://tao-group.com/

The contents of this e-mail and any attachments are confidential and may
be legally privileged. If you have received this e-mail and you are not
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Although we routinely screen for viruses, addressees should scan this
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Re: [linux-lvm] I'm confused

[Pantaleimon]

On Monday 09 December 2002 11:29, William Blunn wrote:
> > I think hardisk manufacturers use base 10, rather than base 2,
> > when they speak of "mega" and "giga", ie. mega = 1000K and not
> > 1024K. That means that a 120G hardisk is only 114.4G.
>
> No.
>
> You are right in that "mega = 1000K", but from your figure of 114.4, you
> still appear to have "K = 1024" and "G = 1024M", both of which are
> wrong.
>

I had G=1000, M=1000 and K=1024 which would give 120 x 10^6 x 1024 =114.4KiB. 
I stand corrected on the matter of me saying/implying K=1024.

I am glad to hear that symbols have been defined for the base 2 multipliers. I 
shall try to use them. I seem to remember reading somthing about it sometime 
ago. Didn't someone propose to use something like KK, MM and GG, too. When I 
tell some people that, even when it comes to computers, the multiplier "kilo" 
formally, if not in practice, means "x 1000" they just won't believe me.


> Hard disk manufacturers use SI defined multipliers, i.e. they use a
> documented standard.
>
>   K = 10^3
>   M = 10^6
>   G = 10^9
>
>   120 GB = 120 000 000 000 B
>
> Computer people have traditionally abused these symbols to mean
> multipliers with similar values, but based on powers of two.
>
> Symbols have been defined for these multipliers, but some people still
> haven't caught up to them.
>
>   Ki = 2^10 = 1024
>   Mi = 2^20 = 1048576
>   Gi = 2^30 = 1073741824
>
> So
>
>   120 GB ~= 111.8 GiB
>
> Interestingly, LVM1's vgdisplay incorrectly uses "GB" in its output
> where it should say "GiB".
>
> Bill