linux-ext4 - Re: [PATCH] e2fsprogs: detect zoned disks and prevent their raw use

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Date:   Fri, 15 Jun 2018 18:36:31 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.com>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Mike Snitzer <snitzer@...hat.com>, hare@...e.de,
        Jens Axboe <axboe@...nel.dk>, mwilck@...e.com,
        Damien Le Moal <damien.lemoal@....com>,
        Bart Van Assche <Bart.VanAssche@....com>
Subject: Re: [PATCH] e2fsprogs: detect zoned disks and prevent their raw use

On Jun 15, 2018, at 6:28 PM, Andreas Dilger <adilger@...ger.ca> wrote:
> 
> On Jun 15, 2018, at 2:56 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
>> 
>> Using raw zoned disks by filesystems requires special handling, only
>> f2fs currently supports this. All other filesystems do not support
>> dealing with zoned disks directly.
>> 
>> As such using raw zoned disks is not supported by e2fsprogs, to use them you
>> need to use dm-zoned-tools, format them with dzadm, set the scheduler to
>> deadline, and then setup a dmsetup with zoned type, and somehow set
>> this up on every boot to live a semi-happy life for now.
>> 
>> Even if you use dmsetup on every boot, the zoned disk is still exposed,
>> and a user may still think they have to run mkfs.ext[234] on it instead
>> of the /dev/mapper/ disk, and then mount it by mistake.
>> 
>> In either case you may seem to believe your disk works and only eventually
>> end up with alignmet issues and perhaps lose you data. For instance the
>> below was observed with XFS but its expected ext[234] users would see
>> the same:
> 
> If you are interested in ext4 and SMR drives, there were some patches
> developed to allow ext4 to work on zoned disks, essentially converting
> it to be a "lazy-journal log-structured" filesystem.  That makes almost
> all of the filesystem IO linear (though we could avoid duplicate journal
> writes by writing large IOs directly to disk).
> 
> This was presented at FAST'17 as "ext4-lazy", though I'm unable to find the
> patch that implemented this feature (it is not landed in the kernel yet).
> 
> Maybe Ted could send out a URL for the patch, even if it is a WIP?

To reply to my own email, I found the patch in question:

https://github.com/tytso/ext4-patch-queue/blob/master/add-ext4-journal-lazy-mount-option

it wasn't showing up in any of my searching.


Cheers, Andreas






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