iSCSI Performance Experiments

1
iSCSI Performance Experiments

• Li Yin
• EECS Department
• U.C.Berkeley

2
Outline

• Introduction
• iSCSI
• iSCSI Performance Challenges
• Experimental Plan

3
Introduction

• Networked Shared Storage
• In contrast to direct attached storage
• High availability
• Better resource sharing
• Easy to manage
• NAS vs. SAN

4
IP SAN

• Transport SCSI over IP Networks
• Less cost
• Longer operating distance
• Leverage existing technology and management
  tools
• Protocols to transport SCSI over IP Networks
• FCIP , iFCP ,iSCSI

5
iSCSI

• Encapsulates SCSI command in TCP packets
• SCSI commands are encapsulated into iSCSI
  protocol data unit (PDU).
• PDUs are sent over one or more TCP connections.
• TCP as the transport protocol
• Provides the reliability and congestion control
  method
• The most dominant transport protocol
• Well-supported

6
iSCSI Performance Challenges

• TCP processing overhead
• Security
• Packet drops
• Delay caused by long distance

7
Experiments Setup

• Testbed
• Initiator
• Intel initiator
• Router
• Current NistNet controls delay, bandwidth and
  drop rate
• Future Router VM
• Target
• DiskSim as the iSCSI target

8
Experimental Plan

• Performance Metrics
• Throughput
• I/O Rate
• Three steps
• iSCSI on a separated LAN
• iSCSI on a LAN with cross traffic
• iSCSI on a WAN

9
Preliminary result

• To test the impact of packet drop, delay and
  request size on the overall throughput.
• Setup
• Ignore the disk mechanical impact
• Delay 10ms
• Bandwidth 100Mb/s
• NistNet to generate random drop
• Continuously write/read (100 times) equal size
  request to/from the target

10
Delay vs Throughput
(ms)
11
Drop Rate vs. Throughput
12
Experimental Plan (Cont.)

• Issues to focus on
• How to maintain a high performance with packet
  drops?
• Performance drop due to
• Bandwidth shrink
• Head of Queue blocking
• Bandwidth provision?
• Might be expensive.
• Router queue management mechanism with the
  assistance of PNE?
• Multiple TCP Connections?
• Higher overall bandwidth.
• Smart scheduling?

13
Experimental Plan (cont.)

• How to achieve high performance with a long
  delay?
• Proxy?
• Cache /Pre-fetching?
• Initiator buffer?
• Avoid retransmission?