When you mark an out-of-threshold item as resolved, the Alert Center ignores the item until the sample period does not include the time the item was resolved. This gives you one full sample period to fix the problem.
For example, you have a disk utilization threshold with a sample time period of 1 day, and a polling interval of 1 hour. At 1:00 p.m. on Tuesday, you see that a device has exceeded the percentage specified in the threshold. At 1:05 p.m., you mark that item as resolved and make a note to go out and get more disk space for the device.
If before 1:05 p.m. on Wednesday, you have purchased and installed more drive space on the device, the item does not reappear in the list of out of threshold items the next time the Alert Center checks the database at 2:00 p.m.. Likewise, if you have forgotten and did not update the device with more disk space, the item reappears in the list of out of threshold items the next time the Alert Center checks the database, even though you marked it as resolved on Tuesday.
In another example, you have an SNMP trap threshold with a sample period of 1 hour, and a polling interval of 30 minutes. At 1:00 p.m. the Alert Center checks the database for the 12:00 p.m. to 1:00 p.m. hour, and finds that a device has exceeded the number of SNMP traps specified in the threshold. You see the item and update it as resolved at 1:10 p.m..
The next time the Alert Center checks the database at 1:30 p.m., it ignores the item you have marked as resolved. If by 2:00 p.m., you have turned off the SNMP trap agent on the offending device, the item does not reappear in the list of out of threshold items. Likewise, if you have not taken steps to fix the problem, the item reappears in the list of out of threshold items even though you previously marked it as resolved.
Note: This method of resolving items does not apply to the WhatsUp Health threshold.