Antw: Re: [EXT] Concurrent usage of iscsiadm
>>> The Lee-Man schrieb am 21.10.2021 um 17:55 in Nachricht <8d711f1e-d3f4-4109-87ed-a950e93298...@googlegroups.com>: > Hi Ulrich: > > I don't see how systemd is going to run parallel iscsiadm commands, at > least with the units that come with open-iscsi. Systemd actually guards > against that. Actually my statement was not specific to iscsiadm, but general: If serveral systemd services depend on one systemd target, those services are started in parallel (unless other conditions prevent that) when that target is to be reached. > > As far as locking, I'd be glad to entertain/discuss/review patches that > make iscsiadm behave well when run in parallel. But such as change isn't on > my short list of things to work on, since I don't really see the need. I'd > rather focus on making iscsid play well in containers. > > On Wednesday, October 20, 2021 at 11:19:24 PM UTC-7 Uli wrote: > >> Hi! >> >> Another thing is: Whether you like systemd or not: It runs many processes >> automatically and concurrently. >> So it seems wise that iscasadm may be run concurrently. If there are >> issues, iscsiadm should use a MUTEX internally to avoid those IMHO >> >> Regards, >> Ulrich >> >>> Vojtech Juranek schrieb am 20.10.2021 um 08:58 in >> Nachricht <4882593.9...@localhost.localdomain>: >> > Hi, >> > I'd like to follow up with discussion about concurrent usage iscsiadm >> tool. >> > It >> > was discussed here about year ago, with suggestion not to use it >> > concurrently >> > [1]. On the other hand, comment [2] says it should be fine. Is the an >> > agreement >> > in open-iscsi community if the concurrent usage of iscsiadm is safe or >> not? >> > If >> > it's not safe, is there any bug for open-iscsi describing the issue and >> > potential problems if iscsiadm is used concurrently? >> > >> > The motivation why I'm popping up this again is that in oVirt project >> [3] we >> > >> > use a lock before calling iscsiadm to make sure it's not run in >> parallel. >> > This >> > causes us various issues (see e.g. BZ #1787192 [2]) and we'd like to get >> rid >> > >> > off this lock. >> > >> > I run several thousands tests with our typical usage of iscsiadm [4], >> > running >> > iscsiadm in parallel and haven't spot any issue so far. This suggests >> > removing >> > the lock can be safe, but of course my tests could be just a pure luck. >> So >> > before removing this lock from our code base, I'd like to know your >> thoughts >> > >> > about it. >> > >> > Thanks >> > Vojta >> > >> > [1] https://groups.google.com/g/open-iscsi/c/OHOdIm1W274/m/9l5NcPQHBAAJ >> > [2] https://bugzilla.redhat.com/show_bug.cgi?id=1787192#c18 >> > [3] https://www.ovirt.org/ >> > [4] https://github.com/oVirt/vdsm/blob/master/tests/storage/stress/ >> > initiator.py >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups >> > "open-iscsi" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an >> > email to open-iscsi+...@googlegroups.com. >> > To view this discussion on the web visit >> > >> > https://groups.google.com/d/msgid/open-iscsi/4882593.9CP3fYhb5E%40localhost.l > >> > ocaldomain. >> >> >> >> >> > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to open-iscsi+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/open-iscsi/8d711f1e-d3f4-4109-87ed-a950e932 > 9895n%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to open-iscsi+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/6172782702A100044BFD%40gwsmtp.uni-regensburg.de.
Re: [EXT] Concurrent usage of iscsiadm
Hi Vojtech: I know there's confusion around this issue, and as some testing at RH has shown, you can get away with using iscsiadm in parallel, as long as you're careful about what you do. For example, if each instance is trying to log into a different target, and there is no error handling occurring, testing seems to show this to be fine. But I continue to recommend against doing this, because (as I've said before) there isn't sufficient locking in iscsiadm to allow completely parallel execution. [By the way, I'm willing to entertain patches that fix that.] Yes, some of the code in iscsiadm is safe for parallel execution, such as talking the iscsid and accessing the node database. But much is not, such as error handling and sysfs access. And there is very little reason to try to login into multiple targets using parallel calls to iscsiadm when iscsiadm now how the "no-wait" option, allowing it to send off login requests without waiting for success or timing out and failing. Bottom line, I'd say using iscsiadm in parallel at your own risk. And if you do so and find issues, then we can try to address them. But the last thing I want for iscsiadm is one giant lock. And locking individual pieces of iscsiadm can lead to deadlock situations, if not sequenced correctly. I hope that answers your questions. On Wednesday, October 20, 2021 at 11:19:24 PM UTC-7 Uli wrote: > Hi! > > Another thing is: Whether you like systemd or not: It runs many processes > automatically and concurrently. > So it seems wise that iscasadm may be run concurrently. If there are > issues, iscsiadm should use a MUTEX internally to avoid those IMHO > > Regards, > Ulrich > >>> Vojtech Juranek schrieb am 20.10.2021 um 08:58 in > Nachricht <4882593.9...@localhost.localdomain>: > > Hi, > > I'd like to follow up with discussion about concurrent usage iscsiadm > tool. > > It > > was discussed here about year ago, with suggestion not to use it > > concurrently > > [1]. On the other hand, comment [2] says it should be fine. Is the an > > agreement > > in open-iscsi community if the concurrent usage of iscsiadm is safe or > not? > > If > > it's not safe, is there any bug for open-iscsi describing the issue and > > potential problems if iscsiadm is used concurrently? > > > > The motivation why I'm popping up this again is that in oVirt project > [3] we > > > > use a lock before calling iscsiadm to make sure it's not run in > parallel. > > This > > causes us various issues (see e.g. BZ #1787192 [2]) and we'd like to get > rid > > > > off this lock. > > > > I run several thousands tests with our typical usage of iscsiadm [4], > > running > > iscsiadm in parallel and haven't spot any issue so far. This suggests > > removing > > the lock can be safe, but of course my tests could be just a pure luck. > So > > before removing this lock from our code base, I'd like to know your > thoughts > > > > about it. > > > > Thanks > > Vojta > > > > [1] https://groups.google.com/g/open-iscsi/c/OHOdIm1W274/m/9l5NcPQHBAAJ > > [2] https://bugzilla.redhat.com/show_bug.cgi?id=1787192#c18 > > [3] https://www.ovirt.org/ > > [4] https://github.com/oVirt/vdsm/blob/master/tests/storage/stress/ > > initiator.py > > > > -- > > You received this message because you are subscribed to the Google > Groups > > "open-iscsi" group. > > To unsubscribe from this group and stop receiving emails from it, send > an > > email to open-iscsi+...@googlegroups.com. > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/open-iscsi/4882593.9CP3fYhb5E%40localhost.l > > ocaldomain. > > > > > -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to open-iscsi+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/9b1f3139-8efe-4b1d-aa07-b623c212c9fbn%40googlegroups.com.
Antw: [EXT] Concurrent usage of iscsiadm
Hi! Another thing is: Whether you like systemd or not: It runs many processes automatically and concurrently. So it seems wise that iscasadm may be run concurrently. If there are issues, iscsiadm should use a MUTEX internally to avoid those IMHO Regards, Ulrich >>> Vojtech Juranek schrieb am 20.10.2021 um 08:58 in Nachricht <4882593.9CP3fYhb5E@localhost.localdomain>: > Hi, > I'd like to follow up with discussion about concurrent usage iscsiadm tool. > It > was discussed here about year ago, with suggestion not to use it > concurrently > [1]. On the other hand, comment [2] says it should be fine. Is the an > agreement > in open-iscsi community if the concurrent usage of iscsiadm is safe or not? > If > it's not safe, is there any bug for open-iscsi describing the issue and > potential problems if iscsiadm is used concurrently? > > The motivation why I'm popping up this again is that in oVirt project [3] we > > use a lock before calling iscsiadm to make sure it's not run in parallel. > This > causes us various issues (see e.g. BZ #1787192 [2]) and we'd like to get rid > > off this lock. > > I run several thousands tests with our typical usage of iscsiadm [4], > running > iscsiadm in parallel and haven't spot any issue so far. This suggests > removing > the lock can be safe, but of course my tests could be just a pure luck. So > before removing this lock from our code base, I'd like to know your thoughts > > about it. > > Thanks > Vojta > > [1] https://groups.google.com/g/open-iscsi/c/OHOdIm1W274/m/9l5NcPQHBAAJ > [2] https://bugzilla.redhat.com/show_bug.cgi?id=1787192#c18 > [3] https://www.ovirt.org/ > [4] https://github.com/oVirt/vdsm/blob/master/tests/storage/stress/ > initiator.py > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to open-iscsi+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/open-iscsi/4882593.9CP3fYhb5E%40localhost.l > ocaldomain. -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to open-iscsi+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/6171066602A100044B4B%40gwsmtp.uni-regensburg.de.
