Re: [PATCH v10 12/41] btrfs: implement zoned chunk allocator

[Naohiro Aota <naohiro.aota@wdc.com>]

On Wed, Nov 25, 2020 at 09:59:40AM +0000, Graham Cobb wrote:
>On 25/11/2020 01:57, Naohiro Aota wrote:
>> On Tue, Nov 24, 2020 at 07:36:18PM +0800, Anand Jain wrote:
>>> On 10/11/20 7:26 pm, Naohiro Aota wrote:
>>>> This commit implements a zoned chunk/dev_extent allocator. The zoned
>>>> allocator aligns the device extents to zone boundaries, so that a zone
>>>> reset affects only the device extent and does not change the state of
>>>> blocks in the neighbor device extents.
>>>>
>>>> Also, it checks that a region allocation is not overlapping any of the
>>>> super block zones, and ensures the region is empty.
>>>>
>>>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>>>
>>> Looks good.
>>>
>>> Chunks and stripes are aligned to the zone_size. I guess zone_size won't
>>> change after the block device has been formatted with it? For testing,
>>> what if the device image is dumped onto another zoned device with a
>>> different zone_size?
>>
>> Zone size is a drive characteristic, so it never change on the same device.
>>
>> Dump/restore on another device with a different zone_size should be banned,
>> because we cannot ensure device extents are aligned to zone boundaries.
>
>Does this mean 'btrfs replace' is banned as well? Or is it allowed to a
>similar-enough device? What about 'add' followed by 'remove'?

Replacing is allowed if the zone size is the same. Adding a disk is the
same. This restriction is checked in btrfs_init_new_device() (patch 5).