Add FAILFAST support

ZFS works best when it is notified as soon as possible when a device
failure occurs.  This allows it to immediately start any recovery
actions which may be needed.  In theory Linux supports a flag which
can be set on bio's called FAILFAST which provides this quick
notification by disabling the retry logic in the lower scsi layers.

That's the theory at least.  In practice is turns out that while the
flag exists you oddly have to set it with the BIO_RW_AHEAD flag.
And even when it's set it you may get retries in the low level
drivers decides that's the right behavior, or if you don't get the
right error codes reported to the scsi midlayer.

Unfortunately, without additional kernels patchs there's not much
which can be done to improve this.  Basically, this just means that
it may take 2-3 minutes before a ZFS is notified properly that a
device has failed.  This can be improved and I suspect I'll be
submitting patches upstream to handle this.

1 files changed, 4 insertions, 10 deletions

diff --git a/module/zfs/vdev_disk.c b/module/zfs/vdev_disk.c
index 9ae8fbc18..863392544 100644
--- a/module/zfs/vdev_disk.c
+++ b/module/zfs/vdev_disk.c
@@ -342,15 +342,13 @@ retry:
 	if (dr == NULL)
 		return ENOMEM;
 
+	if (zio && !(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)))
+			bio_set_flags_failfast(bdev, &flags);
+
 	dr->dr_zio = zio;
 	dr->dr_rw = flags;
 	block_size = vdev_bdev_block_size(bdev);
 
-#ifdef BIO_RW_FAILFAST
-	if (flags & (1 << BIO_RW_FAILFAST))
-		dr->dr_rw |= 1 << BIO_RW_FAILFAST;
-#endif /* BIO_RW_FAILFAST */
-
 	/*
 	 * When the IO size exceeds the maximum bio size for the request
 	 * queue we are forced to break the IO in multiple bio's and wait
@@ -434,6 +432,7 @@ int
 vdev_disk_physio(struct block_device *bdev, caddr_t kbuf,
 		 size_t size, uint64_t offset, int flags)
 {
+	bio_set_flags_failfast(bdev, &flags);
 	return __vdev_disk_physio(bdev, NULL, kbuf, size, offset, flags);
 }
 
@@ -540,11 +539,6 @@ vdev_disk_io_start(zio_t *zio)
 		return ZIO_PIPELINE_CONTINUE;
 	}
 
-#ifdef BIO_RW_FAILFAST
-	if (zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD))
-		flags |= (1 << BIO_RW_FAILFAST);
-#endif /* BIO_RW_FAILFAST */
-
 	error = __vdev_disk_physio(vd->vd_bdev, zio, zio->io_data,
 		                   zio->io_size, zio->io_offset, flags);
 	if (error) {