WG: Re: read performance much slower than write

Thanks, I did lots of testing with the following setups:

On local disk (3ware Escalade 9600 with 4 SATA 250GB disks raid 5) on one of
the enbd-servers with reiserfs (same result on 3 other servers):
Version  1.03
     ------Sequential Output------ 
     -Per Chr- --Block-- -Rewrite- 
Size K/sec %CP K/sec %CP K/sec %CP 
  4G 41786  99 79583  29 48658  17 

--Sequential Input- --Random-
-Per Chr- --Block-- --Seeks--
K/sec %CP K/sec %CP  /sec %CP
37161  88 163373  41 263.6  1

      ------Sequential Create------ 
      -Create-- --Read--- -Delete-- 
files  /sec %CP  /sec %CP  /sec %CP 
   16 26591  99 +++++ +++ 22029 100 

--------Random Create--------
-Create-- --Read--- -Delete--
 /sec %CP  /sec %CP  /sec %CP
25958  99 +++++ +++ 20655  99



On one enbd-device (enbd-client) not using raid (/dev/nde only this device
is loaded) with reiserfs:
Version  1.03       
     ------Sequential Output------ 
     -Per Chr- --Block-- -Rewrite- 
Size K/sec %CP K/sec %CP K/sec %CP 
  4G 34954  97 89405  51 20011   6 

--Sequential Input- --Random-
-Per Chr- --Block-- --Seeks--
K/sec %CP K/sec %CP  /sec %CP
26427  65 44505   7 184.8   0

      ------Sequential Create------ 
      -Create-- --Read--- -Delete-- 
files  /sec %CP  /sec %CP  /sec %CP 
   16 24953  99 +++++ +++ 21020 100 

--------Random Create--------
-Create-- --Read--- -Delete--
 /sec %CP  /sec %CP  /sec %CP
24748  99 +++++ +++ 19699 100



On enbd-client using raid5 (/dev/nda /dev/ndb /dev/ndc /dev/ndd)with
reiserfs:
Version  1.03       
     ------Sequential Output------ 
     -Per Chr- --Block-- -Rewrite- 
Size K/sec %CP K/sec %CP K/sec %CP 
  4G 32725  96 70303  43 18766   9

--Sequential Input- --Random-
-Per Chr- --Block-- --Seeks--
K/sec %CP K/sec %CP  /sec %CP
12271  35 12439   3 650.4   2

      ------Sequential Create------ 
      -Create-- --Read--- -Delete-- 
files  /sec %CP  /sec %CP  /sec %CP 
   16 26404  99 +++++ +++ 22008 100 

--------Random Create--------
-Create-- --Read--- -Delete--
 /sec %CP  /sec %CP  /sec %CP
25597 100 +++++ +++ 20470  99


I am using Gigabit Ethernet cards on all servers and client and a D-Link
Gigabit switch.

on the local disks the read operations per block are about twice as fast as
writing. As soon as I start using enbd the performance for read per block is
about half of write. Using software raid cuts it down to 1/7.
The performance per Chr is not breaking in that much.
I also checked if I am using the same blocksize on server and client and I
do.

I searched the logs and could not find anything there.

I am using enbd.conf a both server and client side to start the connection.

enbd.conf server1:
server   backend1  10099 /dev/sdc1 -b 4096
enbd.conf server2:
server   backend2  10199 /dev/sdc1 -b 4096
enbd.conf server3:
server   backend3  10299 /dev/sdc1 -b 4096
enbd.conf server4:
server   backend4  10399 /dev/sdc1 -b 4096

enbd.conf client:
client   backend1  /dev/nda 192.168.100.185 10099 -n 2            -m -e -b
4096
client   backend2  /dev/ndb 192.168.100.186 10199 -n 2            -m -e -b
4096
client   backend3  /dev/ndc 192.168.100.187 10299 -n 2            -m -e -b
4096
client   backend4  /dev/ndd 192.168.100.188 10399 -n 2            -m -e -b
4096


Thanks in advance for your invaluable help,

Christian