Court finds a software cure
Court finds a software cure
District Court in Maine installs Diskeeper utility to combat fragmentation
|Before'and'after images of 20M rows of disk clusters show contiguous files as blue and fragmented ones as red. A Maine District Court found that defragmenting disks reduced file access time.|
By Drew Robb
Special to GCN
To support its ballooning workload, the U.S. District Court in Portland, Maine, expanded from one server running Microsoft Windows NT to five within three years.
After the hardware upgrades, however, users still complained about long delays in accessing files. Directory listings and file openings sometimes took up to 10 seconds, they said.
'One server took 20 minutes to shut down and reboot,' senior automation manager Kevin Beaulieu said. 'System deterioration over time was the reality of the NT world as far as we were concerned.'
Although the newer parts of the network were less affected, performance of all the servers began to deteriorate steadily.
The court investigated the suspects and found the guilty party: disk fragmentation.
Fragmentation in client-server environments results from hundreds of documents constantly being written to and deleted from disks. The file fragments scatter into whatever disk space is immediately available.
The practice saves time that would otherwise be consumed in looking for enough contiguous free space for depositing the files. Although it simplifies writing to disk, it divides documents into thousands of pieces, and for every 1,000 fragments, 1,000 system input/output operations are required to pull them back together.
The original dual 200-MHz Pentium Pro server had three 4G drives. It ran Microsoft Exchange Server, Windows Internet Naming Service, Dynamic Host Configuration Protocol, NT primary domain controller software, Computer Associates International Inc. ARCServe backup software, Corel WordPerfect, and court-specific applications for restitution payments and jury tracking.
After three years, the server's files had become so splintered that some server operations took 25 times longer than normal. 'With the multitude of reboots that NT requires during software installations or configuration changes, fragmentation wasted a great deal of network resources,' Beaulieu said.
The slow performance caused court officials to upgrade the primary domain controller to a dual 450-MHz Pentium II system with 512M of RAM and 52G of RAID Level 5 storage.
It hosts Microsoft Exchange Server, Systems Management Server, NetShow Server and Internet Information Server; Netscape Enterprise Server; fax software from RightFax Inc. of Tucson, Ariz.; and file and print services.Not again
After initially performing well, however, the upgraded server also began to fragment.
The court finally installed network defragmenter software on each server. It checks each file and partition to determine which files need to be defragmented and which should be moved to another location to provide more contiguous free space.
To accomplish this online so that defragmenting could occur in background, the court chose Diskeeper for Windows NT from Executive Software Inc. of Glendale, Calif.
Diskeeper's MoveFile function, developed in cooperation with Microsoft Corp., makes a contiguous copy of a fragmented file to a specified location.
The function changes the file pointers to indicate the new contiguous copy, and then it deallocates the space given to the original file fragments.
From his desk, Beaulieu remotely loaded the defragmenter software onto each server and workstation across the network. He used Diskeeper's proprietary Set It and Forget It option, which schedules online defragmentation for times of minimal system overhead. Some critical files are unsafe to defragment online, such as the master file table and the paging files, although their fragmentation can significantly hurt network responsiveness.
In the NT File System, the master file table maps every file on the volume and is itself a file. Every time a new file is created, a record of it is made in the master file table, which expands as more files are added. Files that constantly grow are susceptible to extreme fragmentation.
Similarly, paging files are at risk in any system that becomes highly fragmented. Because an active paging file is held open for the exclusive use of the NT operating system, online defragmenters cannot access it.Critical condition
Microsoft advises against bypassing NT to defragment the critical files online. Alternatives include offline defragmentation during rebooting.
A new approach in Diskeeper 5.0 prevents fragmentation through a monitoring process called Frag Guard.
If the defragmentation software finds the master file table or paging files are fragmented when it is first installed, it defragments them at boot time and sets Frag Guard to work to keep them from becoming fragmented again.
The Maine court's servers had become so badly fragmented that Diskeeper had to be rerun several times in the beginning.
'The results compared favorably to what I've seen from major hardware upgrades,' Beaulieu said.
He said the time that Diskeeper took to down a server dropped from 20 minutes to 45 seconds, and file access went from five or 10 seconds down to one to three seconds.Drew Robb writes about information technology from Tujunga, Calif.