During a recent hurricane warning, the file servers at the County of Miami’s office in Dade, Fla., began crashing before the first drop of rain hit the beaches. It wasn’t the hurricane’s high winds, or the related flooding and power outages that caused these failures: It was the county’s employees.
Fearing the worst for their desktops after being hit three years in a row by hurricanes, employees developed the habit of copying their desktop computers’ hard drives onto the servers as soon as news about a new hurricane hit the airwaves. Dozens of employees, with desktops averaging four to eight GB, started to copy their desktop data to the servers simultaneously. The servers couldn’t take the pounding.
Not every IT organization has hurricane warnings to worry about. On the other hand, every Windows NT/2000 server systems administrator needs to ensure server availability and performance. Specifically, they need to be concerned about uncontrolled server disk capacity consumption by employees.
Strategic Research Corp., a storage research firm in Santa Barbara, Calif., estimates that disk drive failures in distributed Windows NT networks cause about 55% of all server downtime, as illustrated in Figure 1. This percentage includes failures by servers that have exceeded their capacity. Strategic Research Corp. also estimates that disk space consumption in some organizations has reached rates from 70% to 100% annually. Overloaded capacity can make a server’s performance suffer.
Overloaded Capacity Can Lead to Failure
Short of a complete server crash, any employee can seriously compromise server performance and application availability by storing large files on servers shared by other employees. Some systems administrators deal with this problem by manually babysitting a server’s capacity level or using load balancing to control the amount of data on a server. A better solution is setting multiple, real-time directory disk quota thresholds on the amount of space assigned to each employee and to each department. Employees should receive automatic alert notifications as they get close to their quota thresholds. This procedure allows systems administrators to allocate storage evenly as a shared resource, and to make sure the types of documents saved conform to the IT department’s policy for what belongs on the server.
Use Soft Quotas to Monitor Server Disk Usage Transparently
Directory quotas enable systems administrators to maintain server performance very easily, and to avoid system crashes due to exceeded capacity levels. Soft quotas allow employees who’ve exceeded their quota threshold to continue to save files on the server. Systems administrators can automatically execute command lines, set alerts to be triggered, run reports, or send the activity to the event log.
Soft quotas provide a good way to monitor the status of any server’s disk usage in relation to the server’s disk capacity. Alerts can provide plenty of warning when a server is about to reach its allowable capacity. Soft quotas are useful for monitoring server disk usage at the 50% to 85% percent range.
On the other hand, soft quotas can work only if the IT department educates and empowers employees in grooming their disk space following a quota threshold alert. Otherwise, quotas will have limited effect on employee’s storage usage.
Enforce Hard Quotas to Ensure Maximum Server Uptime
Unlike soft quotas, hard quotas allow the server to refuse any additional I/O event, such as saving a file, after the quota threshold has been met or exceeded. To this end, hard quotas can ensure a certain percentage of free space for server performance, application availability, and continuity.
A systems administrator can set hard quotas in a variety of expressions, including percentage of available space (such as 89%), fixed quantity (such as 10 GB), or percentage of space currently used (such as 150% of current space used). These expressions provide systems administrators with the flexibility to set the appropriate hard quotas for the particular device and the nature of the data stored on each server.
In addition to setting directory-level hard quotas, systems administrators can set a hard quota on each employee’s space within the directory quotas on specific servers. This practice can prevent employees from jeopardizing server performance. If the sum of each employee’s individual quota totals less than the overall directory quota, the server is under its total allowable capacity, and performance is maintained. These conditions will hold true even if each user reaches his maximum quota simultaneously.
Setting hard quotas puts the burden on the IT department to make sure employees understand that they have to free up space before they can store additional documents. Thus, the IT department needs to initiate a good communications program before turning on hard quotas. The IT department should also make it easy for employees to groom their space. A hard quota with an overdraft allotment enables employees who’ve exceeded their quota to save their files without any disruptions to their work. As employees receive alerts, the IT department can e-mail them a report listing all their files. For example, an HTML page with file links lets an employee click on a file extension, view the file, and then click on the link again to delete the file.
Windows 2000’s User Quotas Don’t Hold Up
Windows 2000 includes a native user quota management capability. However, with only one quota threshold, employees don’t receive any warning before reaching their quota limitation. Lack of warning can prompt unpleasant calls from employees to the systems administrator or help desk. In addition, Windows 2000’s user quotas don’t allow employees to completely save a file if they’ve reached or exceeded the quota during the save. This procedure can prove disruptive to employees. Windows 2000 server does not include directory quotas, nor does it allow any quota control beyond the user level.
Third-party quota management software companies offer better alternatives than Windows 2000’s native quota management capability. Some products include multiple quota thresholds so employees have plenty of advance warning when they approach their hard quota. Other useful capabilities include providing employees with reports listing their files, or enabling a block mechanism to keep certain files types (such as MP3s) from being stored on the network.
Real-time quota management products don’t do periodic scans, and thus don’t affect a server’s performance. However, a quota management product that scans every five or 10 minutes can put a dent in a server’s performance. Also, with this type of product employees may exceed capacity if they go over their quota after the scan cycle takes place. The CrossLinks sidebar lists third-party quota management vendors for Windows NT/2000. //
Elizabeth M. Ferrarini is a freelance author based in Arlington, Mass.