[linux-lvm] LVM Thin Provisioning size limited to 16 GiB?

[Sebastian Riemer]

On 02/03/12 18:17, Mike Snitzer wrote:
>>
>> I've also tested to explicitly set the --poolmetadatasize to 16 GiB and
>> the data pool to 100 GiB, but same result. I also did some benchmarks.
>> Performance wasn't that bad, but could be really better (at least doubled).
>>
> 
> You haven't actually shown how you attempted to make use of a 100GB and
> 16GB metadatasize.
> 
> But the maximum metadata device size is 17112760320 sectors (or 15.9375
> GB).
> 
> So try with 15GB (even though that is way larger than you need for 100GB
> of data).

I've tried these commands:
    vgcreate test /dev/md/test*
    lvcreate -i 12 -I 64 -L 100G --poolmetadatasize 16G -T test/pool

I don't see any chance to select the meta-data device in LVM like it is
possible with dmsetup.

>> Here are my commands:
>>    vgcreate test /dev/md/test*
>>    lvcreate -i 12 -I 64 -L 16G -T test/pool
>>    lvcreate -V 45G -T test/pool -n test00

This is like it is described in the man page of lvcreate. There it is
documented as a single lvcreate command.

This creates five dm devices in /dev/mapper:
test-pool: 16,106,127,360 Bytes, 254:3, table: 0 31457280 linear 254:2 0

test-pool_tdata: 16,106,127,360 Bytes, 254:1,

table: 0 31457280 striped 12 128 9:127 2048 9:126 2048 9:125 2048 9:124
2048 9:123 2048 9:122 2048 9:121 2048 9:120 2048 9:119 2048 9:118 2048
9:117 2048 9:116 2048

test-pool_tmeta: 4,194,304 Bytes, 254:0, table: 0 8192 linear 9:116 2623488

test-pool-tpool: 16,106,127,360 Bytes, 254:2
table: 0 31457280 thin-pool 254:0 254:1 128 0 0

test-test00: 48,318,382,080 Bytes, 254:4, table: 0 94371840 thin 254:2 1

>> Seems like pool meta-data and pool data aren't separated at current
>> development state.
> 
> But in the above test, you've created a striped LV named /dev/test/pool
> of 16GB.
> 
> And you've written 11GB to the test00 thin device.  And you're running
> out of metadata space.
> 
> This implies to me that LVM2's size guesstimate for the proper data vs
> metadata size split for a 16GB volume isn't conservative enough
> (relative to metadata size).
> 
> Anyway, showing your 'dmsetup table' output would be helpful in the
> future.

The meta-data is on one of the striped devices used for the data. This
is wrong. LVM should support selecting a separate meta-data device!

Sebastian