iSCSI Performance Experiments

Li Yin

EECS Department

U.C.Berkeley

Outline

Introduction iSCSI iSCSI Performance Challenges Experimental Plan

Introduction Networked Shared Storage

In contrast to direct attached storage High availability Better resource sharing Easy to manage

NAS vs. SAN

Network Attached Storage Storage Area Networks

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

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

iSCSI Performance Challenges

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

Experiments Setup Testbed:

Initiator: Intel initiator

Router: Current: NistNet controls delay, bandwidth and drop rate Future: Router VM

Target: DiskSim as the iSCSI target

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

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

Delay vs Throughput

(ms)

Drop Rate vs. Throughput

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?

Experimental Plan (cont.)

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