On 6/14/18 09:11, Luis R. Rodriguez wrote:
> Setting up a zoned disks in a generic form is not so trivial. There
> is also quite a bit of tribal knowledge with these devices which is not
> easy to find.
>
> The currently supplied demo script works but it is not generic enough to be
> practical for Linux distributions or even developers which often move
> from one kernel to another.
>
> This tries to put a bit of this tribal knowledge into an initial udev
> rule for development with the hopes Linux distributions can later
> deploy. Three rule are added. One rule is optional for now, it should be
> extended later to be more distribution-friendly and then I think this
> may be ready for consideration for integration on distributions.
>
> 1) scheduler setup
> 2) backlist f2fs devices
> 3) run dmsetup for the rest of devices
>
> Note that this udev rule will not work well if you want to use a disk
> with f2fs on part of the disk and another filesystem on another part of
> the disk. That setup will require manual love so these setups can use
> the same backlist on rule 2).
>
> Its not widely known for instance that as of v4.16 it is mandated to use
> either deadline or the mq-deadline scheduler for *all* SMR drivers. Its
> also been determined that the Linux kernel is not the place to set this up,
> so a udev rule *is required* as per latest discussions. This is the
> first rule we add.
>
> Furthermore if you are *not* using f2fs you always have to run dmsetup.
> dmsetups do not persist, so you currently *always* have to run a custom
> sort of script, which is not ideal for Linux distributions. We can invert
> this logic into a udev rule to enable users to blacklist disks they know they
> want to use f2fs for. This the second optional rule. This blacklisting
> can be generalized further in the future with an exception list file, for
> instance using INPUT{db} or the like.
>
> The third and final rule added then runs dmsetup for the rest of the disks
> using the disk serial number for the new device mapper name.
>
> Note that it is currently easy for users to make a mistake and run mkfs
> on the the original disk, not the /dev/mapper/ device for non f2fs
> arrangements. If that is done experience shows things can easily fall
> apart with alignment *eventually*. We have no generic way today to
> error out on this condition and proactively prevent this.
>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
> README | 10 +++++-
> udev/99-zoned-disks.rules | 78 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 87 insertions(+), 1 deletion(-)
> create mode 100644 udev/99-zoned-disks.rules
>
> diff --git a/README b/README
> index 65e96c34fd04..f49541eaabc8 100644
> --- a/README
> +++ b/README
> @@ -168,7 +168,15 @@ Options:
> reclaiming random zones if the percentage of
> free random data zones falls below <perc>.
>
> -V. Example scripts
> +V. Udev zone disk deployment
> +============================
> +
> +A udev rule is provided which enables you to set the IO scheduler, blacklist
> +driver to run dmsetup, and runs dmsetup for the rest of the zone drivers.
> +If you use this udev rule the below script is not needed. Be sure to mkfs only
> +on the resulting /dev/mapper/zone-$serial device you end up with.
> +
> +VI. Example scripts
> ==================
>
> [[
> diff --git a/udev/99-zoned-disks.rules b/udev/99-zoned-disks.rules
> new file mode 100644
> index 000000000000..e19b738dcc0e
> --- /dev/null
> +++ b/udev/99-zoned-disks.rules
> @@ -0,0 +1,78 @@
> +# To use a zone disks first thing you need to:
> +#
> +# 1) Enable zone disk support in your kernel
> +# 2) Use the deadline or mq-deadline scheduler for it - mandated as of v4.16
> +# 3) Blacklist devices dedicated for f2fs as of v4.10
> +# 4) Run dmsetup other disks
> +# 5) Create the filesystem -- NOTE: use mkfs /dev/mapper/zone-serial if
> +# you enabled use dmsetup on the disk.
> +# 6) Consider using nofail mount option in case you run an supported kernel
> +#
> +# You can use this udev rules file for 2) 3) and 4). Further details below.
> +#
> +# 1) Enable zone disk support in your kernel
> +#
> +# o CONFIG_BLK_DEV_ZONED
> +# o CONFIG_DM_ZONED
> +#
> +# This will let the kernel actually see these devices, ie, via fdisk /dev/sda
> +# for instance. Run:
> +#
> +# dmzadm --format /dev/sda
> +
> +# 2) Set deadline or mq-deadline for all disks which are zoned
> +#
> +# Zoned disks can only work with the deadline or mq-deadline scheduler. This is
> +# mandated for all SMR drives since v4.16. It has been determined this must be
> +# done through a udev rule, and the kernel should not set this up for disks.
> +# This magic will have to live for *all* zoned disks.
> +# XXX: what about distributions that want mq-deadline ? Probably easy for now
> +# to assume deadline and later have a mapping file to enable
> +# mq-deadline for specific serial devices?
> +ACTION=="add|change", KERNEL=="sd*[!0-9]", ATTRS{queue/zoned}=="host-managed", \
> + ATTR{queue/scheduler}="deadline"
> +
> +# 3) Blacklist f2fs devices as of v4.10
> +# We don't have to run dmsetup on on disks where you want to use f2fs, so you
> +# can use this rule to skip dmsetup for it. First get the serial short number.
> +#
> +# udevadm info --name=/dev/sda | grep -i serial_shor
> +# XXX: To generalize this for distributions consider using INPUT{db} to or so
> +# and then use that to check if the serial number matches one on the database.
> +#ACTION=="add", SUBSYSTEM=="block", ENV{ID_SERIAL_SHORT}=="XXA1ZFFF", GOTO="zone_disk_group_end"
> +
> +# 4) We need to run dmsetup if you want to use other filesystems
> +#
> +# dmsetup is not persistent, so it needs to be run on upon every boot. We use
> +# the device serial number for the /dev/mapper/ name.
> +ACTION=="add", KERNEL=="sd*[!0-9]", ATTRS{queue/zoned}=="host-managed", \
> + RUN+="/sbin/dmsetup create zoned-$env{ID_SERIAL_SHORT} --table '0 %s{size} zoned $devnode'", $attr{size}
> +
> +# 4) Create a filesystem for the device
> +#
> +# Be 100% sure you use /dev/mapper/zone-$YOUR_DEVICE_SERIAL for the mkfs
> +# command as otherwise things can break.
> +#
> +# XXX: preventing the above proactively in the kernel would be ideal however
> +# this may be hard.
> +#
> +# Once you create the filesystem it will get a UUID.
> +#
> +# Find out what UUID is, you can do this for instance if your zoned disk is
> +# your second device-mapper device, ie dm-1 by:
> +#
> +# ls -l /dev/disk/by-uuid/dm-1
> +#
> +# To figure out which dm-$number it is, use dmsetup info, the minor number
> +# is the $number.
> +#
> +# 5) Add an etry in /etc/fstab with nofail for example:
> +#
> +# UUID=99999999-aaaa-bbbb-c1234aaaabbb33456 /media/monster xfs nofail 0 0
> +#
> +# nofail will ensure system boots fine even if you boot into a kernel which
> +# lacks support for the device and so it is not found. Since the UUID will
> +# always match the device we don't care if the device moves around the bus
> +# on the system. We just need to get the UUID once.
> +
> +LABEL="zone_disk_group_end"
Applied. Thanks Luis !
--
Damien Le Moal,
Western Digital
