[Xen-users] XEN HVMs on LVM over iSCSI - test results, (crashes) and questions

[Ivan Porro <pivan@xxxxxxxxxxxxx>]

Hi all,

some results from my configuration.

I've this configuration (I'm not interested in raw top performances but 
in reliability.. so, I can accept slow MB/sec and prefer to rely on a 
RAID6, for example):
1 Infortrend iSCSI Array A16E-G2130-4 with:
- 1GB DDR cache
- RAID6
- 7 x 500GB sataII Seagate ST3500630NS with 16mb (no budget for SAS)
- one of the logic volumes (about 1TB) is actually bounded to a single 
channel
1 DELL PE1950 server with:
- QLogic iSCSI HBA QLA 4060C
- 2 x Quad core x5335  2GHz Xeon
- 8GB RAM
- 2 x 73GB SAS drives (raid1 software)

1 DELL 2716 gigabit switch in the middle

The array, tha HBA and the switch are Jumbo frame enabled. CHAP 
authentication enabled.
I've successfully installed XEN 3.1.0 from source (kernel 2.6.18-xen) 
and the QLogic ISP4XXX iSCSI Host Bus Adapter driver 5.01.00.08-2.
I have successfully installed a windows XP HVM, a Scientific Linux CERN 
- SLC - 4 and 3 (RedHat EL 4 and 3) HVMs and other non HVM machines.
The volume I imported from the iSCSI is used with LVM: each HVM domain 
has a 8GB drive partitioned with a 1GB swap and rest on /.
These are performance for bonnie++ (Per Chr column write and read):

iSCSI      dom0: w: 54M, r: 47M  (no domU)

Local disk dom0: w: 59M, r: 51M  (3 idle domU)

HVM single     : w: 18M, r: 37M

I've then launched bonnie++ on two separate SLC4 HVM (cloned):

HVM 1          : w:  8M,   r: 33M
HVM 2          : w:  8.5M, r: 38M

The same on three HVM:

HVM 1          : w:  4.4M, r: 11M
HVM 2, crashed, lost ssh, error: "hda: lost interrupt", need "xm reboot"
HVM 3, crashed, lost ssh, error: "hda: lost interrupt", need "xm reboot"


So, where is the limit of my configuration?

How can this scale up in your opinions in real applications (not just 
stressing it with bonnie++)?
I'm quite confident that HVM performance should be slow. My problem 
eventually is that iSCSI performance are not so bad compared on Local 
disk performance (which could lead to a "really poor local disk perf!").
Any suggestion on this is appreciated.


Thank you in advance,

        Ivan




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