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EdgeWare™ GIS

EdgeWare iSCSI: Optimizing Storage for Google's Fusion

Introduction

EdgeWare version 3 (EW3) is delivering network attached storage for geographical information system (GIS) including Google's Fusion servers.  To date, EW3 offered NFS as a file serving protocol to access network storage solutions for Fusion.  In an effort to reduce the time for transmission of raw data to the networked storage and provide IPSAN capabilities, EW3.1 introduces iSCSI as a flexible solution that scales for performance for a single Fusion server.

IPSAN Architecture: iSCSI is Network Direct Attach Storage System

EW3 iSCSI target software provides multiple connections per session (MCS) and scales from a single gigabit per second (Gb/s) network connection at 123 MB/s sequential writing to five Gb/s connections for a maximum  sequential write throughput of greater than 400 MB/s (see Illustration 1).  NFS connectivity on a single Gb/s network connection provides a maximum of 70 MB/s for sequential writes and cannot scale well with bonding.  EW iSCSI targets also scale well with a 10 Gb/s network connection up to 600 MB/s.  The best NFS asynchronous sequential writes over a 10 Gb/s connection are about 200 MB/s in practice.

Scalability of iSCSI for Efficiency

With either MCS or 10 Gb, the iSCSI protocol between the Fusion server and data storage provides at least a 3:1 performance improvement for copying raw data from the Fusion server to the networked storage.  During the processing, the Fusion server also performs better when moving data to and from the iSCSI storage compared to NFS.  Additionally, the iSCSI performance is not impacted as much as NFS for small reads and writes as iSCSI carries less overhead.  Thus, the time required for data preparation and final data serving is reduced.

Network Benefits of iSCSI over Direct Attach

The other benefit of iSCSI is that the storage looks exactly like it is local storage but has network location flexibility.  All administrative commands for local disk storage are honored by the iSCSI target.  Thus, a Fusion server administrator benefitss from the local storage administration but retains the flexibility of locating the storage away from the Fusion server itself.  Additionally, the networked storage is accessible read-only to offer the final data over the Fusion web server.  For the web serving, iSCSI sequential reads offer better end-user visual experiences over NFS.

Bringing the iSCSI Storage Solution to Fusion Servers

The Google Fusion software requires no modifications to benefit from the iSCSI storage.

Fusion Storage Architecture with iSCSI

The iSCSI target is attached to the Fusion server using an iSCSI initiator.  For Linux Fusion servers, we recommend Open-iSCSI, a software Open Source Software initiator.  The Open-iSCSI initiator group reports 550 MB/s over a 10 Gb/s connection (http://www.open-iscsi.org).

Case Study: Using Fusion on SuSE v9.3

Cutting Edge has used iSCSI as the basis for doing a Fusion server configuration with SuSE v9.3 as the host operating system.  The configuration worked as expected with no issues.  In this case, the EW support team updated the SuSE 9.3 kernel to a SuSE v10.x released kernel with the Open-iSCSI kernel modules.  The optimum architecture used XFS on the iSCSI target and placed the journal on local storage.

Illustration 1: iSCSI Performance with Gb NIC Additions for MCS

 

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