Date: Tue, 19 Jun 2018 11:03:43 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Don Lewis <truckman@FreeBSD.org> Cc: "rc@freebsd.org" <rc@freebsd.org>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org> Subject: Re: review of nfsd rc.d script patch Message-ID: <YTOPR0101MB0953E37C78966A4FB54C71E0DD700@YTOPR0101MB0953.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <tkrat.dc869fdc2002b320@FreeBSD.org> References: <YTOPR0101MB0953A6D3081676510290AEEFDD7C0@YTOPR0101MB0953.CANPRD01.PROD.OUTLOOK.COM>, <tkrat.dc869fdc2002b320@FreeBSD.org>
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Don Lewis wrote:
>On 15 Jun, Rick Macklem wrote:
>> Hi,
>>
>> For the pNFS service MDS machine, the nfsd can't be started until all nf=
s mounts
>> in /etc/fstab are done.
>> I think that adding "mountcritremote" to the "# REQUIRE:" line is suffic=
ient to do this?
>>
>> I don't think delaying the startup of the nfsd daemon until after any NF=
S mounts
>> are done will do any harm, but if others think it would be a POLA violat=
ion,
>> I could make this dependent on the pNFS service being enabled.
>> Does anyone think this would cause a POLA violation?
>
>Sounds like that would break cross mounts. Back in the olden days
>before the automounter, I would set up workstation clusters with hosta
>exporting local filesystem /home/hosta, and hostb exporting /home/hostb.
>In addition, hosta would do a bg NFS mount of /home/hostb and hostb
>would do a bg NFS mount of /home/hosta. That way everybody would have a
>consistent view of everything. If a power failure took down everything,
>the first system up would export its local filesystem and even though it
>wouldn't be able to mount any remote filesystems, mount would background
>itself at the boot would complete. As the remaining machines came up,
>they would be able to mount the remote filesystems of the machine that
>came up earlier, and the early machines would mount the filesystems from
>the later machines as they became available.
>
>If nfsd is delayed until all the NFS filesystems are mounted, the above
>setup would deadlock.
I think you would have used the "bg" mount option on the NFS mounts to get
the above to work? (That is what makes the mount go "background" if it can'=
t
contact the NFS server.)
If so, this would still behave the same after this patch.
The patch forces "mountcritremote" to complete before nfsd is run (to be ho=
nest,
since "m" comes before "n", I think that happens anyhow? This patch just tr=
ies to
ensure that).
It does not force waiting for mount completion if "bg" is specified.
(Put another way, "bg" can't be used for mounts of DSs for the pNFS server =
setup.)
rick
ps: I recall a small company that only had a few SGI workstations and did a=
setup
like the above. However, they weren't very good at configuring it and=
, as such,
everyone would run around for a half hour after a power failure, tryi=
ng to get
the workstations back up;-)
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