Re: DOMU Disk I/O

["Gary Duzan" <gary%duzan.org@localhost>]

In Message <50D41AB6.1050809%citrix.com@localhost>,
   =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau%citrix.com@localhost>wrote:

=>On 21/12/12 06:28, Cherry G. Mathew wrote:
=>> On 10 December 2012 01:09,  <gary%duzan.org@localhost> wrote:
=>>>    I've been running a NetBSD VPS at prgmr.com for several years
=>>> now, and generally been pleased. However, recently I've noticed
=>>> that my disk I/O rates have been rather bad. The upgrade to 6.0_STABLE
=>>> was rather slow, and I regularly see "systat vm" report xbd0 %busy
=>>> at 100% with only a handful of transfers and sometimes under 100K
=>>> bytes. Is this likely to be a problem with the 6.0 DOMU or something
=>>> on the DOM0? Should I consider going back to 5.2?
=>>>
=>> 
=>> Hi Gary,
=>> 
=>> Are you running MP by any chance ? roger@ did some benchmarks and
=>> there were no significant i/o related performance issues, so I'm
=>> curious.
=>
=>I've done some testing in the past, but it was only with big files. If
=>you are working with a large set of small files you may experience
=>slowdown. For example decompressing a src.tar.gz snapshot can take
=>around ~30min, while it takes less than 2 minutes on a Linux DomU (using
=>the same Dom0). I've reported this on another thread, but I haven't had
=>time to debug this any further
=>(http://mail-index.netbsd.org/tech-kern/2012/10/29/msg014249.html). Do
=>you know by any change the Dom0 OS and kernel version?
=>

   Thanks for the responses. I ran into another prgmr user on IRC
with a fresh NetBSD 6.0 DOMU on a different DOM0, and he agreed to
run the same test as I did, and his results were fine. To make
things as simple as possible, I just ran dd against the swap
partition, and while booted into the installer, when practical.
Here are the notes from the tests (with minor edits for accuracy):

===========================================================================
(16:58:32) floam: how are you doing the tests? I'm shelled into a NetBSD 6.0 
domU I just got going a few days ago at the moment, if you want to compare.
(17:06:32) floam: # dd if=/dev/rxbd0b of=/dev/null count=5000
(17:06:33) floam: 5000+0 records in
(17:06:33) floam: 5000+0 records out
(17:06:33) floam: 2560000 bytes transferred in 1.422 secs (1800281 bytes/sec)
(17:06:45) floam: # dd if=/dev/zero of=/dev/rxdb0b count=5000
(17:06:45) floam: 5000+0 records in
(17:06:45) floam: 5000+0 records out
(17:06:45) floam: 2560000 bytes transferred in 0.049 secs (52244897 bytes/sec)
(17:08:55) floam: that's on a booted, installed 6.0, on a 256MB vps on 
fuller.prgmr.com

(17:10:35) Gary @ Freenode6: I'm on a 512MB vps on crock. New numbers in a 
minute.
(17:10:57) Gary @ Freenode6: # dd if=/dev/rxbd0b of=/dev/null count=5000
(17:10:57) Gary @ Freenode6: 5000+0 records in
(17:10:58) Gary @ Freenode6: 5000+0 records out
(17:10:58) Gary @ Freenode6: 2560000 bytes transferred in 27.185 secs (94169 
bytes/sec)
(17:12:56) Gary @ Freenode6: Mine is a 6.0_STABLE from October 18. I'm building 
a newer stable now, and I'll also test with a release installer.
(17:13:11) Gary @ Freenode6: # dd if=/dev/zero of=/dev/rxbd0b count=5000
(17:13:11) Gary @ Freenode6: 5000+0 records in
(17:13:11) Gary @ Freenode6: 5000+0 records out
(17:13:11) Gary @ Freenode6: 2560000 bytes transferred in 180.504 secs (14182 
bytes/sec)

kern.version = NetBSD 6.0_STABLE (XEN3_DOMU) #2: Thu Oct 18 14:45:35 EDT 2012
        root@wheel:/raid/netbsd-6/src/sys/arch/amd64/compile/obj/XEN3_DOMU
# dd if=/dev/rxbd0b of=/dev/null count=5000
5000+0 records in
5000+0 records out
2560000 bytes transferred in 35.006 secs (73130 bytes/sec)
# dd if=/dev/zero of=/dev/rxbd0b count=5000
5000+0 records in
5000+0 records out
2560000 bytes transferred in 187.015 secs (13688 bytes/sec)

kern.version = NetBSD 6.0 (INSTALL_XEN3_DOMU)
# dd if=/dev/rxbd0b of=/dev/null count=5000
5000+0 records in
5000+0 records out
2560000 bytes transferred in 27.574 secs (92841 bytes/sec)
# dd if=/dev/zero of=/dev/rxbd0b count=5000
5000+0 records in
5000+0 records out
2560000 bytes transferred in 174.441 secs (14675 bytes/sec)
===========================================================================

   I believe they use CentOS for the DOM0 servers, but I didn't
get an immediate response on IRC to confirm. At this point I've
asked prgmr.com support to look into any issues on the DOM0 server.

   Thanks.

                                        Gary Duzan