kern/107975: NFS TCP read slow - write fast

Wolfgang Hurst whurst at whurst.net
Tue Jan 16 08:30:20 UTC 2007


>Number:         107975
>Category:       kern
>Synopsis:       NFS TCP read slow - write fast
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Jan 16 08:30:19 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Wolfgang Hurst
>Release:        FreeBSD 6.x
>Organization:
Tiscali
>Environment:
FreeBSD xxx.xxxx.xxx 6.2-STABLE FreeBSD 6.2-STABLE #3: Tue Jan 16 07:52:22 CET 2007     root at xxx.xxxxx.xxx:/usr/obj/usr/src/sys/XXXX  i386

>Description:

Server :
 s1 -> FreeBSD 6.2-STABLE (Intel) my private fileserver
 s2 -> FreeBSD 6.1-PRERELEASE (Dec 2006) customer fileserver

Clients :
 c1 -> Solaris 8 (latest patches) my private client
 c2 -> Linux RE4 customer client

I have problems with TCP NFS mounts. Read requests are very very very slow. On 100Mb/s network
i have approx. 300 kb/s. On Gigabit ethernet i reach only 10 Mb/s.

TCP write requests are fast with full speed of storage. on 100 Mb/s i have 90 Mb/s. On Gigabit network i have 150-200 Mb/s (storage speed)

I saw this problem once and i fix this -> change to UDP. with UDP is anything fine. fullspeed in both directions.

i googling but i found nothing about this problem. i think i'm the only one with this problem and i think -> the hardware sucks ... switching to UDP is fine -> forget it ...

BUT yesterday a customer want tcp mount with an full difference freesbd and client. and he got the same problem. tcp ist slow on read but fast on write. on a full difference equickment.

i have freebsd 5.x somewhere, on this server works anything fine. but since freebsd 6.x the nfs-tcp makes some problems.

yes you can say .> mount via udp, but this is not possible, because udp mounts uses to many kernel memory and my private server rans out of memory. the kernel sad : "ENOMEM at bla" when he try to access the SATA devices. on linux the udp nfs crashes the host. it's uncool.

i try to test many many sysctl values, but nothing helps.

i think it's not a hardware problem, maybe the em (intel ethernet) device is broken. but rsync or other tcp services runns with full speed, it's only (nfs AND tcp AND freebsd6.x AND nfs-server)

i know you have many other stuff to do, but somethink ist there very very strange. somewho should be look at this (maybe someone speak german :-)))))

>How-To-Repeat:
fresh install (server and client)
export something on freebsd 6.x nfs server
mount on client (solaris 8 or linux re4)
transfer files
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:


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