Date: Thu, 6 Feb 2020 12:06:25 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: freebsd-scsi@freebsd.org Cc: Jim Harris <jimharris@freebsd.org>, "Kenneth D. Merry" <ken@FreeBSD.org> Subject: Re: [wtf] vtscsi aka virtio_scsi does not see disk at target 7 Message-ID: <b6227561-0e84-f614-bca1-36e42379115f@FreeBSD.org> In-Reply-To: <c0e529c8-a111-4caa-37a9-5b447abb9a2a@FreeBSD.org>
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By the way, quite a long time ago, on Wed Sep 26 00:57:10 UTC 2012 Jim Harris
<jimharris@freebsd.org> suggested this:
> I'm wondering if the scsi_xpt.c code
> should instead (or also) ignore the initiator_id if cpi->transport ==
> XPORT_SAS? initiator_id isn't really valid for SAS transport.
I think that that proposal still makes sense and we should go for it.
Any objections?
On 16/01/2020 17:27, Andriy Gapon wrote:
>
> I think I see what's going on, but it was a WTF moment for me.
>
> We use virtio_scsi driver on GCE VMs. We typically configure VMs with 6 or less
> disks, but recently we started to use VMs with 8+ disks. On some of them, after
> a reboot, one disk is missing. Here is an example:
>
> # camcontrol devlist -v
> scbus0 on vtscsi0 bus 0:
> <Google PersistentDisk 1> at scbus0 target 1 lun 0 (pass0,da0)
> <Google PersistentDisk 1> at scbus0 target 2 lun 0 (pass1,da1)
> <Google PersistentDisk 1> at scbus0 target 3 lun 0 (pass2,da2)
> <Google PersistentDisk 1> at scbus0 target 4 lun 0 (pass3,da3)
> <Google PersistentDisk 1> at scbus0 target 5 lun 0 (pass4,da4)
> <Google PersistentDisk 1> at scbus0 target 6 lun 0 (pass5,da5)
> <Google PersistentDisk 1> at scbus0 target 8 lun 0 (pass6,da6)
> <Google PersistentDisk 1> at scbus0 target 9 lun 0 (pass7,da7)
>
> We noticed that it is always target 7 that is missing.
>
> After looking at the code, the problem is kind of obvious.
> scsi_scan_bus:
> for (i = low_target; i <= max_target; i++) {
> cam_status status;
>
> if (i == initiator_id)
> continue;
>
> vtscsi_cam_path_inquiry:
> cpi->initiator_id = VTSCSI_INITIATOR_ID;
>
> /*
> * Specification doesn't say, use traditional SCSI default.
> */
> #define VTSCSI_INITIATOR_ID 7
>
> From what I see, on GCE at least, target 7 is a valid target and it is not
> reserved for the initiator. At the same time, I see that target 0 is never used
> for disks. Also, it seems that virtio configuration gives 253 as the maximum
> target ID on those instances.
>
> I would appreciate any suggestions on what to use for initiator_id in this
> driver. Thanks!
>
--
Andriy Gapon
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