The online auctioneer, which suffered a site outage for nearly 11 hours Wednesday, said the interruption resulted from a series of failures that affected both the company's primary and backup systems. The San Jose, Calif.-based company restored its Web site at 10 p.m. PST Wednesday.
The outage "was compounded by a decision to delay the replacement of certain hardware components in an effort to avoid disrupting service during the busy holiday season," read a letter from company chief executive Meg Whitman that was posted on eBay's announcements board.
"While we have known for awhile that a potential problem existed in our shared disk hardware, we chose to delay the recommended upgrade because we had developed a series of work-arounds that had previously proven effective. We apologize to you all for this lengthy interruption of service," Whitman said in the letter.
eBay said it will extend by 24 hours all auctions affected by the outage and credit all associated fees.
The site's prolonged inaccessibility provoked a flurry of comments and questions from eBay watchers to CNET News.com.
Gartner analyst Donna Scott says people and process issues cause 80 percent of unplanned downtime, so Web sites can't solve chronic outages simply by installing more hardware and adding redundancy.
Although eBay has been hit by system problems in the past, Wednesday's outage marked the first in months to last more than two hours. The company, which recently kicked off a national advertising campaign, implemented a backup system late last year after a slew of multi-hour outages that plagued the popular Web site in 1999.
The company said that since the 1999 disruptions, it has invested heavily in additional hardware and the new backup system. For the last four quarters, eBay boasted 99 percent uptime.
But recent uptime may have rested on some unsteady shoulders. In explaining Wednesday's troubles, eBay said it had "known for a while that a potential problem existed in our shared disk hardware," but had chosen "to delay the recommended upgrade because we had developed a series of work-arounds that had previously proven effective."
The company said it plans to upgrade some hardware components in the next few weeks, a move that will require scheduled downtime of approximately six hours. eBay said it has also begun a longer-term program to distribute a database to several separate servers that will help isolate any failure to a limited part of the site.
eBay expects the program to be completed within four months.
In early trading Thursday, shares of eBay edged downward $2.34, or nearly 6 percent, to $37.