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...
The other problem is that with two devices we need to be able to stitch
them together in an automated fashion, eg via a systemd service or udev
rule.
But for this we need to be able to identify the devices, which means
both need to carry metadata, and both need to have unique identifier
within the metadata. Which the current metadata doesn't allow to.
Hence my plan is to implement a v2 metadata, carrying UUIDs for the dmz
set _and_ the component device. With that we can update blkid to create
links etc so that the devices can be identified in the system.
Additionally I would be updating dmzadm to write the new metadata.
And I will add a new command 'start' to dmzadm which will then create
the device-mapper device _with the correct size_. It also has the
benefit that we can create the device-mapper target with the UUID
specified in the metadata, so the persistent device links will be
created automatically.
Bob, can you send me your improvements to dmzadm so that I can include
them in my changes?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
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