On 3/25/20 9:02 AM, Damien Le Moal wrote:
On 2020/03/25 15:47, Hannes Reinecke wrote:
On 3/25/20 7:29 AM, Damien Le Moal wrote:
On 2020/03/24 20:04, Bob Liu wrote:
This patch implemented metadata support for regular device by:
- Emulated zone information for regular device.
- Store metadata at the beginning of regular device.
| --- zoned device --- | -- regular device ||
^ ^
| |Metadata
zone 0
Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
---
drivers/md/dm-zoned-metadata.c | 135 +++++++++++++++++++++++++++++++----------
drivers/md/dm-zoned-target.c | 6 +-
drivers/md/dm-zoned.h | 3 +-
3 files changed, 108 insertions(+), 36 deletions(-)
Having thought about it some more, I think we cannot continue with this
'simple' approach.
The immediate problem is that we lie about the disk size; clearly the
metadata cannot be used for regular data, yet we expose a target device
with the full size of the underlying device.
Making me wonder if anybody ever tested a disk-full scenario...
Current dm-zoned does not do that... What is exposed as target capacity is
number of chunks * zone size, with the number of chunks being number of zones
minus metadata zones minus number of zones reserved for reclaim. And I did test
disk full scenario (when performance goes to the trash bin because reclaim
struggles...)
Thing is, the second number for the dmsetup target line is _supposed_ to
be the target size.
Which clearly is wrong here.
I must admit I'm not sure what device-mapper will do with a target
definition which is larger than the resulting target device ...
Mike should know, but it's definitely awkward.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
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