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Re: higher agcount on LVM2 thinp volumes

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: higher agcount on LVM2 thinp volumes
From: Chris Murphy <lists@xxxxxxxxxxxxxxxxx>
Date: Thu, 29 Aug 2013 21:29:14 -0600
Cc: xfs@xxxxxxxxxxx, "stan@xxxxxxxxxxxxxxxxx Hoeppner" <stan@xxxxxxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <289A5A42-9879-4A2A-9284-4B8529A1488D@xxxxxxxxxxxxxxxxx>
References: <321D1F95-5603-4571-A445-A267DA5F670F@xxxxxxxxxxxxxxxxx> <52200BAE.1060501@xxxxxxxxxxx> <4393C3B8-8C46-41ED-B9F3-BC7B37C2681F@xxxxxxxxxxxxxxxxx> <52200F5A.9050702@xxxxxxxxxxx> <289A5A42-9879-4A2A-9284-4B8529A1488D@xxxxxxxxxxxxxxxxx>
On Aug 29, 2013, at 9:24 PM, Chris Murphy <lists@xxxxxxxxxxxxxxxxx> wrote:

> On Aug 29, 2013, at 9:19 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
>> Argh sorry, how did I type THAT?
>> # blockdev --getiomin --getioopt /dev/mapper/vg1-data
> conventional LV:
> [root@f19s ~]# blockdev --getiomin --getioopt /dev/mapper/vg1-data
> 512
> 0
> thinp LV:
> [root@f19s ~]# blockdev --getiomin --getioopt /dev/mapper/vg1-data
> 512
> 262144

It's tied to the chunk size of the thinp. If I create a 4MB chunk size, ioopt 
goes up to match it. The default is 256KB, which reflects the values above.

[root@f19s ~]# lvcreate -L 400G --type thin-pool -c 4M --thinpool thinp vg1
  device-mapper: remove ioctl on  failed: Device or resource busy
  Logical volume "thinp" created
[root@f19s ~]# lvcreate -V 100G -T vg1/thinp --name data
  Logical volume "data" created
[root@f19s ~]# blockdev --getiomin --getioopt /dev/mapper/vg1-data

Chris Murphy
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