On 5/9/25 4:08 PM, Martin Wilck wrote:
Please support this claim with actual numbers. I'm not saying that it's
wrong (it makes sense that John's argument "the round-robin path
selector is inefficient in cases where there is a difference in latency
between paths" applies to all implementations), but you can't present
numbers for one technology and simply apply them to a different
technology without providing any evidence for the latter.
I'd accept this statement in a weaker form, like "It is reasonable to
assume that the same effects would be measured with dm-multipath over
SCSI devices, too".
Marzinski did some tests time ago:
git show c015b1281
commit c015b128103e7a6426d124a38cd679a181573b88
Author: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
Date: Sat Jan 12 00:04:40 2013 -0600
multipath: change default path_selector to
My testing has showed service-time to be as good and occassionally
noticeably better than round-robin. So the patch switches the
default selector to give better performance out of the box.
Signed-off-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
diff --git a/libmultipath/defaults.h b/libmultipath/defaults.h
index f647ee08..097c66f7 100644
--- a/libmultipath/defaults.h
+++ b/libmultipath/defaults.h
@@ -1,7 +1,7 @@
#define DEFAULT_UID_ATTRIBUTE "ID_SERIAL"
#define DEFAULT_UDEVDIR "/dev"
#define DEFAULT_MULTIPATHDIR "/" LIB_STRING "/multipath"
-#define DEFAULT_SELECTOR "round-robin 0"
+#define DEFAULT_SELECTOR "service-time 0"
#define DEFAULT_ALIAS_PREFIX "mpath"
#define DEFAULT_FEATURES "0"
#define DEFAULT_HWHANDLER "0"
I didn't do any test, sorry.
