<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii"> <META NAME="Generator" CONTENT="MS Exchange Server version 6.5.7650.21"> <TITLE>IO error on DM device</TITLE> </HEAD> <BODY>  Hi Alasdair, We are seeing an IO error problem on a DM device, when the HBA ports of another host, seen through the same switch are disabled/enable. We are not understanding on why the paths are failed when ports on other hosts are disabled. Please explain. Below is the problem description and steps to reproduce. Problem : I/O Error on DM device on one host when HBA ports of another host are disabled. OS distros : RHEL4.0 U2/U3. HOW-TO reproduce the problem: 1. Configure 2 storage arrays (A1, A2) and two host (H1, H2) in the same zone, so that both the hosts can see both the arrays. Create and present LUNs (L1, L2) from array (A1) to host (H1) 2. Stop the multipathd daemon (for testing purpose on why the IO error when ports of other hosts are failed). Not stopping it may take long time to reproduce the problem. 3. Start I/O on DM device representing luns L1 and L2 on host H1. We used dt tool for IO exercising. 4. Disable host ports of host H2 or any port of array A2 one after the other (few times) OR disable and enable the same port of the other host – few times (may be 4-5 times). 5. Application (dt tool) aborts with IO error on host H1. ===== Snippet of sys log output (while doing I/O on /dev/dm-0) Feb 1 11:47:14 apwtest52 kernel: SCSI error : <2 0 0 1> return code = 0x20000 Feb 1 11:47:14 apwtest52 kernel: end_request: I/O error, dev sda, sector 1584600 Feb 1 11:47:14 apwtest52 kernel: device-mapper: dm-multipath: Failing path 8:0. <=================path failed, after disabling/enabling the H2 host port 1 Feb 1 11:47:14 apwtest52 kernel: end_request: I/O error, dev sda, sector 1584608 Feb 1 11:47:45 apwtest52 kernel: SCSI error : <3 0 1 1> return code = 0x20000 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sdg, sector 861400 Feb 1 11:47:45 apwtest52 kernel: device-mapper: dm-multipath: Failing path 8:96. <=================path failed, after disabling/enabling the H2 host port 2 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sdg, sector 861408 Feb 1 11:47:45 apwtest52 kernel: SCSI error : <3 0 0 1> return code = 0x20000 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 452760 Feb 1 11:47:45 apwtest52 kernel: device-mapper: dm-multipath: Failing path 8:64. <=================path failed after disabling/enabling the H2 host port 1 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 452768 Feb 1 11:47:45 apwtest52 kernel: SCSI error : <3 0 0 1> return code = 0x20000 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 453784 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 453792 Feb 1 11:47:45 apwtest52 kernel: SCSI error : <3 0 0 1> return code = 0x20000 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 454808 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 454816 Feb 1 11:47:45 apwtest52 kernel: SCSI error : <3 0 0 1> return code = 0x20000 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 863960 Feb 1 11:47:45 apwtest52 kernel: end_request: I/O error, dev sde, sector 863968 Feb 1 11:48:40 apwtest52 kernel: SCSI error : <2 0 1 1> return code = 0x20000 Feb 1 11:48:40 apwtest52 kernel: end_request: I/O error, dev sdc, sector 935384 Feb 1 11:48:40 apwtest52 kernel: device-mapper: dm-multipath: Failing path 8:32. <================= after disabling/enabling the H2 host port 2 Feb 1 11:48:40 apwtest52 kernel: end_request: I/O error, dev sdc, sector 935392 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116924 <============All path to the device /dev/dm-0 failed Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116925 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116926 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116927 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116928 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116929 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116930 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116931 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116932 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116933 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116934 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116935 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116936 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116937 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116938 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116939 Feb 1 11:48:40 apwtest52 kernel: Buffer I/O error on device dm-0, logical block 116940 Observations : As we do the port failure on the other host, paths of the dm device is failed and the subsequent port (i.e A2 or H2 ports) disabling/enabling results into more numbers of path failure and that leads into all path failure condition, which in turn results into IO error on RHEL4.0 U2/U3. Through the device-mapper debug driver we are finding that the there is no valid path in __choose_pgpath() and m->current_pgpath (m is pointer to struct multipath) is null when it comes to map_io() in dm-mpath.c. Another observation is that we are not seeing any IO errors when the same test is executed on SLES9 SP3/SP4. Please provide some pointers on why we are seeing this behavior or is this a known thing at this point in time? Thanks and regards -Murthy </BODY> </HTML>