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Re: [dm-devel] A thin-p over 256 GiB fails with I/O errors with non-power-of-two chunk



On Fri, Jan 18 2013 at  5:19am -0500,
Daniel Browning <db kavod com> wrote:

> Why do I get the following error, and what should I do about it? When I 
> create a raid0 md with a non-power-of-two chunk size (e.g. 1152K instead of 
> 512K), then create a thinly-provisioned volume that is over 256 GiB, I get 
> the following dmesg error when I try to create a file system on it:
> 
>     "make_request bug: can't convert block across chunks or bigger than 1152k 4384 127"
> 
> This bubbles up to mkfs.xfs as
> 
>     "libxfs_device_zero write failed: Input/output error"
> 
> What I find interesting is that it seems to require all three conditions 
> (chunk size, thin-p, and >256 GiB) in order to fail. Without those, it seems 
> to work fine:
> 
>     * Power-of-two chunk (e.g. 512K), thin-p vol, >256 GiB? Works.
>     * Non-power-of-two chunk (e.g. 1152K), thin-p vol, <256 GiB? Works.
>     * Non-power-of-two chunk (e.g. 1152K), regular vol, >256 GiB? Works.
>     * Non-power-of-two chunk (e.g. 1152K), thin-p vol, >256 GiB? FAIL.
> 
> Attached is a self-contained test case to reproduce the error, version 
> numbers, and an strace. Thank you in advance,
> --
> Daniel Browning
> Kavod Technologies
> 
> Appendix A. Self-contained reproduce script
> ===========================================================
> dd if=/dev/zero of=loop0.img bs=1G count=150; losetup /dev/loop0 loop0.img
> dd if=/dev/zero of=loop1.img bs=1G count=150; losetup /dev/loop1 loop1.img
> mdadm --create /dev/md99 --verbose --level=0 --raid-devices=2 \
>       --chunk=1152K /dev/loop0 /dev/loop1
> pvcreate /dev/md99
> vgcreate test_vg /dev/md99
> lvcreate --size 257G --type thin-pool --thinpool test_thin_pool test_vg
> lvcreate --virtualsize 257G --thin test_vg/test_thin_pool --name test_lv
> mkfs.xfs /dev/test_vg/test_lv
> 
> # That is where the error occurs. Next is cleanup.
> lvremove -f /dev/test_vg/test_lv
> lvremove -f /dev/mapper/test_vg-test_thin_pool
> vgremove -f test_vg
> pvremove /dev/md99
> mdadm --stop /dev/md99
> mdadm --zero-superblock /dev/loop0 /dev/loop1
> losetup -d /dev/loop0 /dev/loop1
> rm loop*.img

Limits of the raid0 device (/dev/md99):
cat /sys/block/md99/queue/minimum_io_size
1179648
cat /sys/block/md99/queue/optimal_io_size
2359296

Limits of the thin-pool device (/dev/test_vg/test_thin_pool):
cat /sys/block/dm-9/queue/minimum_io_size
512
cat /sys/block/dm-9/queue/optimal_io_size
262144

Limits of the thin-device device (/dev/test_vg/test_lv):
cat /sys/block/dm-10/queue/minimum_io_size
512
cat /sys/block/dm-10/queue/optimal_io_size
262144

I notice that lvcreate is not using a thin-pool chunksize that matches
the raid0's chunksize (just uses the lvm2 default of 256K).

Switching the thin-pool lvcreate to use --chunksize 1152K at least
enables me to format the filesystem.

And both the thin-pool and thin device have an optimal_io_size that
matches the chunk_size of the underlying raid volume:

cat /sys/block/dm-9/queue/optimal_io_size
1179648
cat /sys/block/dm-10/queue/optimal_io_size
1179648

I'm still investigating the limits issue when --chunksize 1152K isn't
used for the thin-pool lvcreate.


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