<!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 6.5.7652.24"> <TITLE>Enabling/disabling BIO_RW_FAILFAST at load time</TITLE> </HEAD> <BODY>  Hi Christophe and All, During I/O on a path, the paths are marked as failed at DM Multipath, when the I/O returns with Error status as 0x20000 (host code 0x2 denotes DID_BUS_BUSY). What we understand here is, since I/O on multipath devices have BIO_RW_FAILFAST set(hence REQ_FASTFAIL ), retries are not allowed at SCSI mid layer for errors such as QUEUEFULL, UNDERRUN....(as captured in the below syslog snippet) syslog snippet ******************* May 23 16:51:49 lnx kernel: sd 2:0:3:8: SCSI error: return code = 0x20000 May 23 16:51:49 lnx kernel: end_request: I/O error, dev sdfg, sector 4188002 May 23 16:51:49 lnx kernel: end_request: I/O error, dev sdfg, sector 4188008 May 23 16:51:49 lnx kernel: device-mapper: dm-multipath: Failing path 130:32. May 23 16:51:49 lnx kernel: sd 2:0:3:8: SCSI error: return code = 0x20000 May 23 16:51:49 lnx kernel: end_request: I/O error, dev sdfg, sector 4188302 May 23 16:51:49 lnx kernel: end_request: I/O error, dev sdfg, sector 4188303 May 23 16:52:00 lnx kernel: sd 1:0:2:12: SCSI error: return code = 0x20000 As an option we can have user configurable BIO_RW_FAILFAST for enabling and disabling which allows scsi mid layer to retry for I/0 . Below is the patch for passing parameter at load time with DM multipath module for enabling/disabling BIO_RW_FAILFAST flag. * Flag can be set On/Off as follows modprobe dm-multipath fastfailbit=0 //seting it off modprobe dm-multipath fastfailbit=0 //seting it on * By default the flag is kept on. It can also be set from modprobe.conf as : options dm_multipath fastfailbit=0 Please comment !! *************************************** diff -Naur linux-2.6.18.x86_64-orig/drivers/md/dm-mpath.c linux- 2.6.18.x86_64/drivers/md/dm-mpath.c --- linux-2.6.18.x86_64-orig/drivers/md/dm-mpath.c 2007-08-27 02:18:51.000000000 +0530 +++ linux-2.6.18.x86_64/drivers/md/dm-mpath.c 2007-09-12 16:02:29.000000000 +0530 @@ -19,6 +19,7 @@ #include <linux/slab.h> #include <linux/time.h> #include <linux/workqueue.h> +#include <linux/moduleparam.h> #include <asm/atomic.h> #define DM_MSG_PREFIX "multipath" @@ -107,6 +108,7 @@ static void process_queued_ios(void *data); static void trigger_event(void *data); +static int fastfailbit = 1; /*fastfail bit set on by default*/ /*----------------------------------------------- * Allocation routines @@ -800,7 +802,7 @@ dm_bio_record(&mpio->details, bio); map_context->ptr = mpio; - bio->bi_rw |= (1 << BIO_RW_FAILFAST); + bio->bi_rw |= (fastfailbit << BIO_RW_FAILFAST); r = map_io(m, bio, mpio, 0); if (r < 0 || r == DM_MAPIO_REQUEUE) mempool_free(mpio, m->mpio_pool); @@ -1340,6 +1342,10 @@ { int r; + /* validating fastfailbit */ + if(fastfailbit) + fastfailbit=1; + /* allocate a slab for the dm_ios */ _mpio_cache = kmem_cache_create("dm_mpath", sizeof(struct mpath_io), 0, 0, NULL, NULL); @@ -1387,6 +1393,8 @@ module_init(dm_multipath_init); module_exit(dm_multipath_exit); +module_param(fastfailbit, int, 0); +MODULE_PARM_DESC(fastfailbit, "FASTFAIL bit flag "); MODULE_DESCRIPTION(DM_NAME " multipath target"); MODULE_AUTHOR("Sistina Software <<A HREF="mailto:dm-devel@redhat.com">dm-devel@redhat.com</A>>"); MODULE_LICENSE("GPL"); ****************************** Thanks, Vijay Kumar [Kumar, Vijay (STSD)] mailto: vijay.kumar7@hp.com </BODY> </HTML>