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Old 09-28-2010, 09:44 PM
Phillip Susi
 
Default dm-thinp: new device mapper target to thin provision storage

On 9/28/2010 4:49 PM, Heinz Mauelshagen wrote:
>
> These are 2 new device mapper targets "thinp" and "thinp-dev"
> implemented in one module, which allow for thin provisioning of storage
> on a single host from a storage pool to an arbitrary amount of devices.

How is this different than snapshotting a zero target?

> +Create an ext4 filesystem on the thin provisioned device:
> +mkfs -t ext4 /dev/mapper/thinp1

FYI, that tends to spend a lot of time writing hundreds of mb of zeros
to the inode tables, allocating chunks from the backing store. You
might want to add -E lazy_itable_init to stop that.

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Old 09-29-2010, 06:29 AM
Hannes Reinecke
 
Default dm-thinp: new device mapper target to thin provision storage

Phillip Susi wrote:
> On 9/28/2010 4:49 PM, Heinz Mauelshagen wrote:
>> These are 2 new device mapper targets "thinp" and "thinp-dev"
>> implemented in one module, which allow for thin provisioning of storage
>> on a single host from a storage pool to an arbitrary amount of devices.
>
> How is this different than snapshotting a zero target?
>
Main difference is that you actually can free up space.
You can't with snapshotting as then a rollback
becomes impossible.

Cheers,

Hannes
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hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)

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Old 09-29-2010, 11:25 AM
Heinz Mauelshagen
 
Default dm-thinp: new device mapper target to thin provision storage

On Tue, 2010-09-28 at 17:44 -0400, Phillip Susi wrote:
> On 9/28/2010 4:49 PM, Heinz Mauelshagen wrote:
> >
> > These are 2 new device mapper targets "thinp" and "thinp-dev"
> > implemented in one module, which allow for thin provisioning of storage
> > on a single host from a storage pool to an arbitrary amount of devices.
>
> How is this different than snapshotting a zero target?

Like Hanness mentioned: you can free space.

>
> > +Create an ext4 filesystem on the thin provisioned device:
> > +mkfs -t ext4 /dev/mapper/thinp1
>
> FYI, that tends to spend a lot of time writing hundreds of mb of zeros
> to the inode tables, allocating chunks from the backing store. You
> might want to add -E lazy_itable_init to stop that.

Thanks for the hint, I waned to have load on the thin provisioned
devices so far for testing but will have a look at the reduced
allocations with this option.

>
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Old 09-29-2010, 11:25 AM
Heinz Mauelshagen
 
Default dm-thinp: new device mapper target to thin provision storage

On Wed, 2010-09-29 at 08:29 +0200, Hannes Reinecke wrote:
> Phillip Susi wrote:
> > On 9/28/2010 4:49 PM, Heinz Mauelshagen wrote:
> >> These are 2 new device mapper targets "thinp" and "thinp-dev"
> >> implemented in one module, which allow for thin provisioning of storage
> >> on a single host from a storage pool to an arbitrary amount of devices.
> >
> > How is this different than snapshotting a zero target?
> >
> Main difference is that you actually can free up space.
> You can't with snapshotting as then a rollback
> becomes impossible.
>

Yes, that's right.

Heinz

> Cheers,
>
> Hannes


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Old 09-29-2010, 01:41 PM
Phillip Susi
 
Default dm-thinp: new device mapper target to thin provision storage

On 9/29/2010 7:25 AM, Heinz Mauelshagen wrote:
> On Tue, 2010-09-28 at 17:44 -0400, Phillip Susi wrote:
>> How is this different than snapshotting a zero target?
>
> Like Hanness mentioned: you can free space.

Could you clarify that a bit? Is space only freed if you reduce the
length of a device? You can't do the same with a snapshot?

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Old 09-29-2010, 03:20 PM
Heinz Mauelshagen
 
Default dm-thinp: new device mapper target to thin provision storage

On Wed, 2010-09-29 at 09:41 -0400, Phillip Susi wrote:
> On 9/29/2010 7:25 AM, Heinz Mauelshagen wrote:
> > On Tue, 2010-09-28 at 17:44 -0400, Phillip Susi wrote:
> >> How is this different than snapshotting a zero target?
> >
> > Like Hanness mentioned: you can free space.
>
> Could you clarify that a bit? Is space only freed if you reduce the
> length of a device? You can't do the same with a snapshot?

Not just when you shrink a device, you can release all allocations to an
inactive thin provisioned device as well.

With snapshots the exception store is dropped when you delete the
snapshot as well.

But you can't drop allocated space of a partial exception store because
the exception size is much smaller than the allocation units lvm2 goes
by (ie. extents sized 128MB). Thus dropping exceptions related to a now
past EOD segment within the origin just gives you stale exceptions in
the table w/o the option to reduce allocated space.

>
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