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From:   Jianlin Lv <iecedge@gmail.com>
Date:   Sat, 24 Jun 2023 19:45:36 +0800
Message-ID: <CAFA-uR_jk6jCmf9DTebSVBRwtoLuXuyvf1Biq+OObqRVAOZbBw@mail.gmail.com>
Subject: Re: [PATCH] scsi: sd: support specify probe type of build-in driver
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     jejb@linux.ibm.com, martin.petersen@oracle.com, paulmck@kernel.org,
        bp@suse.de, peterz@infradead.org, will@kernel.org,
        rdunlap@infradead.org, kim.phillips@amd.com, rostedt@goodmis.org,
        wyes.karny@amd.com, jianlv@ebay.com, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-scsi@vger.kernel.org
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On Fri, Jun 9, 2023 at 12:23=E2=80=AFAM Bart Van Assche <bvanassche@acm.org=
> wrote:
>
> On 6/7/23 19:51, Jianlin Lv wrote:
> > On Thu, Jun 8, 2023 at 1:07=E2=80=AFAM Bart Van Assche <bvanassche@acm.=
org> wrote:
> >> On 6/7/23 08:55, Jianlin Lv wrote:
> >> 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 inst=
ruct
> > 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 la=
rge
> > number of work nodes.
> Please consider using the paths available in /dev/disk/by-path.

Sorry for the late reply.
I carefully checked the server in the production environment and found
some corner cases where there are differences in the dev/disk/by-path/ of
nodes with the same SKU. These differences are caused by inconsistent
target_numbers.

For example:

diff -y aa-by-path bb-by-path
pci-0000:86:00.0-scsi-0:3:86:0 -> ../../sda |
pci-0000:86:00.0-scsi-0:3:88:0 -> ../../sda
pci-0000:86:00.0-scsi-0:3:87:0 -> ../../sdb |
pci-0000:86:00.0-scsi-0:3:89:0 -> ../../sdb
pci-0000:86:00.0-scsi-0:3:88:0 -> ../../sdc |
pci-0000:86:00.0-scsi-0:3:90:0 -> ../../sdc
pci-0000:86:00.0-scsi-0:3:89:0 -> ../../sdd |
pci-0000:86:00.0-scsi-0:3:91:0 -> ../../sdd
pci-0000:86:00.0-scsi-0:3:90:0 -> ../../sde |
pci-0000:86:00.0-scsi-0:3:92:0 -> ../../sde
pci-0000:86:00.0-scsi-0:3:92:0 -> ../../sdf |
pci-0000:86:00.0-scsi-0:3:93:0 -> ../../sdf
pci-0000:86:00.0-scsi-0:3:93:0 -> ../../sdg |
pci-0000:86:00.0-scsi-0:3:94:0 -> ../../sdg
pci-0000:86:00.0-scsi-0:3:94:0 -> ../../sdh |
pci-0000:86:00.0-scsi-0:3:95:0 -> ../../sdh

I'm still not sure what causes the target_numbers to be different.
However, the existence of such corner cases makes /dev/disk/by-path
unusable for the volume provisioner, similar to /dev/disk/by-id/.

So, If it's not possible to configure disk serialization detection, then
it seems that implementing predictable disk names is the only option.

Jianlin

>
> Thanks,
>
> Bart.