[dm-devel] [PATCH 15/15] dm-zoned: metadata version 2

[Hannes Reinecke]

On 5/11/20 10:36 AM, Damien Le Moal wrote:
> On 2020/05/11 17:24, Hannes Reinecke wrote:
>> Implement handling for metadata version 2. The new metadata adds
>> a label and UUID for the device mapper device, and additional UUID
>> for the underlying block devices.
>> It also allows for an additional regular drive to be used for
>> emulating random access zones. The emulated zones will be placed
>> logically in front of the zones from the zoned block device, causing
>> the superblocks and metadata to be stored on that device.
>> The first zone of the original zoned device will be used to hold
>> another, tertiary copy of the metadata; this copy carries a
>> generation number of 0 and is never updated; it's just used
>> for identification.
>>
>> Signed-off-by: Hannes Reinecke <hare at suse.de>
>> Reviewed-by: Bob Liu <bob.liu at oracle.com>
>> Reviewed-by: Damien Le Moal <damien.lemoal at wdc.com>
> 
> Forgot to read through the documentation update. A couple of comments added below.
> 
>> ---
>>   .../admin-guide/device-mapper/dm-zoned.rst         |  34 ++-
>>   drivers/md/dm-zoned-metadata.c                     | 310 +++++++++++++++++----
>>   drivers/md/dm-zoned-target.c                       | 185 ++++++++----
>>   drivers/md/dm-zoned.h                              |   7 +-
>>   4 files changed, 427 insertions(+), 109 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/device-mapper/dm-zoned.rst b/Documentation/admin-guide/device-mapper/dm-zoned.rst
>> index 7547ce635161..553752ea2521 100644
>> --- a/Documentation/admin-guide/device-mapper/dm-zoned.rst
>> +++ b/Documentation/admin-guide/device-mapper/dm-zoned.rst
>> @@ -37,9 +37,13 @@ Algorithm
>>   dm-zoned implements an on-disk buffering scheme to handle non-sequential
>>   write accesses to the sequential zones of a zoned block device.
>>   Conventional zones are used for caching as well as for storing internal
>> -metadata.
>> +metadata. It can also use a regular block device together with the zoned
>> +block device; in that case the regular block device will be split logically
>> +in zones with the same size as the zoned block device. These zones will be
>> +placed in front of the zones from the zoned block device and will be handled
>> +just like conventional zones.
>>   
>> -The zones of the device are separated into 2 types:
>> +The zones of the device(s) are separated into 2 types:
>>   
>>   1) Metadata zones: these are conventional zones used to store metadata.
>>   Metadata zones are not reported as useable capacity to the user.
>> @@ -127,6 +131,13 @@ resumed. Flushing metadata thus only temporarily delays write and
>>   discard requests. Read requests can be processed concurrently while
>>   metadata flush is being executed.
>>   
>> +If a regular device is used in conjunction with the zoned block device,
>> +a third set of metadata (without the zone bitmaps) is written to the
>> +start of the zoned block device. This metadata has a generation counter of
>> +'0' and will never be updated during normal operation; it just serves for
>> +identification purposes. The first and second copy of the metadata
>> +are located at the start of the regular block device.
>> +
>>   Usage
>>   =====
>>   
>> @@ -138,12 +149,21 @@ Ex::
>>   
>>   	dmzadm --format /dev/sdxx
>>   
>> -For a formatted device, the target can be created normally with the
>> -dmsetup utility. The only parameter that dm-zoned requires is the
>> -underlying zoned block device name. Ex::
>>   
>> -	echo "0 `blockdev --getsize ${dev}` zoned ${dev}" | \
>> -	dmsetup create dmz-`basename ${dev}`
>> +If two drives are to be used, both devices must be specified, with the
>> +regular block device as the first device.
> 
> Actually, the zoned block device must be first. Otherwise dmzadm complains. We
> can change that, or change the doc. Which do you prefer ? No strong opinion here.
> 
Nope, not any more. Fixed it in my local repo (which I haven't pushed, 
sorry).

But after the last discussion we had I thought it better and more 
consistent to have the regular device first, just like the device-mapper 
interface.

>> +
>> +Ex::
>> +
>> +	dmzadm --format /dev/sdxx /dev/sdyy
>> +
>> +
>> +Fomatted device(s) can be started with the dmzadm utility, too.:
>> +
>> +Ex::
>> +
>> +	dmzadm --start /dev/sdxx /dev/sdyy
> 
> And same here, the zoned device must come first. I added a patch that internally
> reverse that order for the dm start operation so that the regular device is
> specified first.
> 
See above. I've fixed up dmzadm for this.

I just hadn't pushed the patch as I wanted to get the kernel bits 
settled. But now that we have I'll be pushing the dm-zoned-tools updates.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare at suse.de                               +49 911 74053 688
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