A method is used in analyzing drive errors in data storage systems. An error tag and total good I/O count are maintained for a drive. For each failed I/O, the following is performed. An error weight per error is retrieved. A new error tag is calculated from the error weight, a previous error tag, and the total good I/O count. An error ratio is calculated from the new error tag and a total I/O count. The error ratio is compared with thresholds. If one or more of the thresholds has been crossed, action is taken on the drive. The error tag is reduced as good I/O is produced.