[linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[Chris Friesen]

Hi,

I'm running the 3.14 kernel with lvm 2.02.98 and I ran into something unexpected 
with lvresize.

I created a sparse volume:

lvcreate -L 25M -V 50M -n sparsevol myvg


This gives output in lvdisplay like this:
   LV Size                52.00 MiB
   Current LE             13
   COW-table size         28.00 MiB
   COW-table LE           7

I then resized the volume with lvresize:

lvresize -L 200M myvg/sparsevol


This seems to resize the COW-table, but not the volume itself.  Now lvdisplay shows:

   LV Size                52.00 MiB
   Current LE             13
   COW-table size         200.00 MiB
   COW-table LE           50


At this point I've got 200MiB of backing store and running "lvs" shows an LSize 
of "200m" but I can only write 52MiB worth of data to the volume before it 
complains.

Is there a way to expand the "LV Size" shown in lvdisplay so that I can write 
the resized amount of data to the volume?

Thanks,
Chris

Re: [linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[Alexey]

Hello,

If you look at the output of `lvs myvg`, then you will understand whats 
happens.
When you create thin LV without specifying option `-T`, lvm 
automatically created TP for you with size equal to -L option.
And when you resize your sparsevol, your TP (auto name lvol1) still have 
old size.

Regards,
Alexey Mochkin

On 2015-10-14 23:18, Chris Friesen wrote:
> Hi,
> 
> I'm running the 3.14 kernel with lvm 2.02.98 and I ran into something
> unexpected with lvresize.
> 
> I created a sparse volume:
> 
> lvcreate -L 25M -V 50M -n sparsevol myvg
> 
> 
> This gives output in lvdisplay like this:
>   LV Size                52.00 MiB
>   Current LE             13
>   COW-table size         28.00 MiB
>   COW-table LE           7
> 
> I then resized the volume with lvresize:
> 
> lvresize -L 200M myvg/sparsevol
> 
> 
> This seems to resize the COW-table, but not the volume itself.  Now
> lvdisplay shows:
> 
>   LV Size                52.00 MiB
>   Current LE             13
>   COW-table size         200.00 MiB
>   COW-table LE           50
> 
> 
> At this point I've got 200MiB of backing store and running "lvs" shows
> an LSize of "200m" but I can only write 52MiB worth of data to the
> volume before it complains.
> 
> Is there a way to expand the "LV Size" shown in lvdisplay so that I
> can write the resized amount of data to the volume?
> 
> Thanks,
> Chris
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[Zdenek Kabelac]

Dne 15.10.2015 v 09:13 Alexey napsal(a):
> Hello,
>
> If you look at the output of `lvs myvg`, then you will understand whats happens.
> When you create thin LV without specifying option `-T`, lvm automatically
> created TP for you with size equal to -L option.
> And when you resize your sparsevol, your TP (auto name lvol1) still have old
> size.
>

Mixing 2 things together.

Newer lvm2 tools (then reported 2.02.98)  are now creating sparse volumes
as a thin volume in thin-pool.

Old behavior with /dev/zero snapshot is thought still available
either with lvm.conf settings  or using  --type snapshot.

Now back to the  original problem - yep you cannot resize it with tool ATM.

There will be likely added support  for    'lvresize -V+'
(it will work for thin volumes & these sparse snapshot)

Basically adding 'virtual size'.

But it has lower priority ATM (as you may resize thin volumes
with -L, and thus users do not have much troubles with it,
expect the logical meaning looks 'wrong' - as resize of thin
volume does not really 'eat' extents from VG.

If you 'urgently' need  bigger size -

- make sure  modified LVs are rather deactivated.
- 'vgcfgbackup' your vg
- take your favourite text editor (e.g.  vi)
- edit size for your '_vorigin' LV (extent_count = ....)
- edit size for respective hidden 'snapshot0' LV (extent_count = ....)
   (if you have more then one -
    find properly numbered one, the one referencing your _vorigin! -
    those 2 LVs should have equal size)
- 'vgcfgrestore'  your updated metadata
- activate now bigger sized _vorigin
- check  blockdev --getsize64  /dev/vg/sparsevol has new correct size
- enjoy

Regards

Zdenek

Re: [linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[Chris Friesen]

On 10/15/2015 03:24 AM, Zdenek Kabelac wrote:
> Dne 15.10.2015 v 09:13 Alexey napsal(a):
>> Hello,
>>
>> If you look at the output of `lvs myvg`, then you will understand whats happens.
>> When you create thin LV without specifying option `-T`, lvm automatically
>> created TP for you with size equal to -L option.
>> And when you resize your sparsevol, your TP (auto name lvol1) still have old
>> size.
>>
>
> Mixing 2 things together.
>
> Newer lvm2 tools (then reported 2.02.98)  are now creating sparse volumes
> as a thin volume in thin-pool.
>
> Old behavior with /dev/zero snapshot is thought still available
> either with lvm.conf settings  or using  --type snapshot.

Okay, that's interesting.  Do you know when this change went in?

Chris

Re: [linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

[Zdenek Kabelac]

Dne 15.10.2015 v 18:47 Chris Friesen napsal(a):
> On 10/15/2015 03:24 AM, Zdenek Kabelac wrote:
>> Dne 15.10.2015 v 09:13 Alexey napsal(a):
>>> Hello,
>>>
>>> If you look at the output of `lvs myvg`, then you will understand whats
>>> happens.
>>> When you create thin LV without specifying option `-T`, lvm automatically
>>> created TP for you with size equal to -L option.
>>> And when you resize your sparsevol, your TP (auto name lvol1) still have old
>>> size.
>>>
>>
>> Mixing 2 things together.
>>
>> Newer lvm2 tools (then reported 2.02.98)  are now creating sparse volumes
>> as a thin volume in thin-pool.
>>
>> Old behavior with /dev/zero snapshot is thought still available
>> either with lvm.conf settings  or using  --type snapshot.
>
> Okay, that's interesting.  Do you know when this change went in?
>

Version 2.02.112 has configurable setting for this.

Zdenek

[linux-lvm] lvmcache - performance and real life usage?

[John Stoffel]

Hi all,

I've finally upgraded my main server which hosts my home directories
and other files on a bunch of 1Tb and 2Tb disks, all mirrored (triple
mirrors in general since I'm paranoid).

So they're starting to die and give me problems, and it's time to
replace them.  I'm thinking of getting a pair of 500Gb SSDs for
boot/lvmcache and a pair of 4Tb WD Blacks for the backend storage.

I've got some KVM running, NFS home directories, LDAP, samba, etc.
I'm willing to dedicate 256Gb of SSD for cache, but before I do this,
I'm curious to know if anyone else is doing this, and how the
performance is in their setup?

I'm running upto date Debbian Jessie on an AMD Phenom(tm) II X4 945
Processor with 16Gb of RAM and a bunch of internal disks on an LSI 8
port controller.  Been very nice, but my mix of SATA I, II and III
disks are showing their age.

Thanks for the comments,
John