Re: [PATCH] scsi: sd: support specify probe type of build-in driver

[Jianlin Lv]

On Thu, Jun 8, 2023 at 1:07 AM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>
> On 6/7/23 08:55, Jianlin Lv wrote:
> > 1. MegaRAID adapters associated with 24 local disks. The disks are named
> > sequentially as "sda," "sdb," and so on, up to "sdx."
> > 2. STAT controllers associated with the root disk, named "sdy."
> >
> > Both the MegaRAID adapters and the SATA controller (PCH) are accessed via
> > the PCIe bus. In theory, depending on their PCIe bus ID in ascending order,
> > the devices should be initialized in ascending order as well.
>
> Hmm ... I don't think there is anything that prevents the PCIe maintainer
> from changing the PCIe probing behavior from synchronous to asynchronous?
> In other words, I don't think it is safe to assume that PCIe devices are
> always scanned in the same order.
>
> > For cloud deployment, the local volume provisioner detects and creates PVs
> > for each local disk (from sda to sdx) on the host, and it cleans up the
> > disks when they are released.
> > This requires the logical names of the disks to be deterministic.
>
> I see two possible solutions:
> - Change the volume provisioner such that it uses disk references that do
>    not depend on the probing order, e.g. /dev/disk/by-id/...

Yes, The "/dev/disk/by-id/" can uniquely identify SCSI devices. However,
I don't think it is suitable for the volume provisioner workflow.
For nodes of the same SKU , a unified YAML file will be defined to instruct
the volume provisioner on how to manage the local disks.
If use WWID, it would mean that a unique YAML file needs to be defined
for each node. This approach becomes impractical when dealing with a large
number of work nodes.

Jianlin

> - Implement an algorithm in systemd that makes disk names predictable.
>    An explanation of how predictable names work for network interfaces is
>    available here: https://wiki.debian.org/NetworkInterfaceNames. The
>    systemd documentation about predictable network names is available here:
>    https://www.freedesktop.org/software/systemd/man/systemd.net-naming-scheme.html
>
> These alternatives have the advantage that disk scanning remains asynchronous.
>
> Thanks,
>
> Bart.
>