From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Christie Subject: Re: do Symmetrix multipath-tools defaults need update ? or scsi-to-blk errors management ? Date: Wed, 10 Jun 2009 18:34:52 -0500 Message-ID: <4A30431C.3030809@cs.wisc.edu> References: <1766094670.1725191244670599365.JavaMail.root@zimbra16-e3.priv.proxad.net> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------060906060402030408040204" Return-path: In-Reply-To: <1766094670.1725191244670599365.JavaMail.root@zimbra16-e3.priv.proxad.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development Cc: Levy_Jerome@emc.com, linux-scsi@vger.kernel.org List-Id: linux-scsi@vger.kernel.org This is a multi-part message in MIME format. --------------060906060402030408040204 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06/10/2009 04:49 PM, christophe.varoqui@free.fr wrote: > Hi Jerome, > > EMC recently asked my/one-of-your client to active "queue_if_no_path" on Symmetrix logical units, which is not the current default setting in the upstream multipath-tools package. > > I'd like to know if you intent on submitting a patch to change the default setting accordingly, or if you'd rather let the no-queueing default unchanged and work on fixing the root cause of this issue. > > ::: Background information, root cause ::: > > The Symmetrix array proved to return scsi errors io to submitters in certains circumstances (I was told of errors on R1+R2 network link). The linux kernel lacking finesse in the SCSI->DM error reporting ends-up invalidating in turn each path of the multipath before the multipathd daemon gets a chance to revalidate. "queue_if_no_path" being disabled, the io errors ends up in the FS layer and in the userspace submitter. > > ::: error log on a 2.6.9 (rhel 4.7) kernel ::: > For RH 4.9 I did the attached patch. So this error is not fastfailed (upstream does not fastfail this type of error when using dm-multipath now). So now the scsi layer will retry its normal 5 times, then fail. > SCSI error : return code 0x8000002 > current sday: sense key Aborted Command > Additional sense: Internal target failure > end_request: I/O error, dev sday, sector XXXXX > device-mapper: dm-multipath: Failing path 67:32. > > ::: unfortunate side effect of queue_if_no_path ::: > > Activating "queue_if_no_path" is certainly an effecient work-around for this kind of short-lived retriable errors, but this feature compromises data-protection on clusters relying on persistent reservation to fence ios from passive nodes. Ironically, the reason is quite similar : SCSI return codes for reservation conflicts also end up invalidating each path of a multipath, and worse, the io causing the conflict gets queued ! and retried ! until the poor active drops its reservation, unleashing data-corrupting ios from passive node queues on the logical unit. > > ::: error log on a 2.6.29.x kernel for a reservation conflict ::: > > sd h:b:t:l: reservation conflict > sd h:b:t:l: [sdu] Unhandled error code > sd h:b:t:l: [sdu] Result: hostbyte=DID_OK driver_byte=DRIVER_OK,SUGGEST_OK > end_request: I/O error, dev sdu, sector XXXXX > device-mapper: dm-multipath: Failing path 65:64. > > ::: persistent reservation + queue_if_no_path, possible solution ? ::: > > Seems to me scsi_lib.c::scsi_io_completion() should be able to cancel a reservation conflicting io and signal blk_end_request() with no error reported. > I was just about to post new blkerr patches. For this we just wan multipath to fail this IO right away right? So have scsi return some fatal error then dm-multipath will see it and not retry that IO? --------------060906060402030408040204 Content-Type: text/plain; name="dont-failfast-dev-errs.patch" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="dont-failfast-dev-errs.patch" ZGlmZiAtLWdpdCBhL2RyaXZlcnMvc2NzaS9zY3NpX2Vycm9yLmMgYi9kcml2ZXJzL3Njc2kv c2NzaV9lcnJvci5jCmluZGV4IDczMDlmMTIuLmQ1YTMzOTAgMTAwNjQ0Ci0tLSBhL2RyaXZl cnMvc2NzaS9zY3NpX2Vycm9yLmMKKysrIGIvZHJpdmVycy9zY3NpL3Njc2lfZXJyb3IuYwpA QCAtMTM5MCw3ICsxMzkwLDcgQEAgaW50IHNjc2lfZGVjaWRlX2Rpc3Bvc2l0aW9uKHN0cnVj dCBzY3NpX2NtbmQgKnNjbWQpCiAJY2FzZSBDSEVDS19DT05ESVRJT046CiAJCXJ0biA9IHNj c2lfY2hlY2tfc2Vuc2Uoc2NtZCk7CiAJCWlmIChydG4gPT0gTkVFRFNfUkVUUlkpCi0JCQln b3RvIG1heWJlX3JldHJ5OworCQkJZ290byBjaGVja19yZXRyeV9jb3VudDsKIAkJLyogaWYg cnRuID09IEZBSUxFRCwgd2UgaGF2ZSBubyBzZW5zZSBpbmZvcm1hdGlvbjsKIAkJICogcmV0 dXJuaW5nIEZBSUxFRCB3aWxsIHdha2UgdGhlIGVycm9yIGhhbmRsZXIgdGhyZWFkCiAJCSAq IHRvIGNvbGxlY3QgdGhlIHNlbnNlIGFuZCByZWRvIHRoZSBkZWNpZGUK --------------060906060402030408040204 Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline --------------060906060402030408040204--