UNIX for Dummies Questions & Answers

hi.. newbie here, just wonder why there is a need for mirroring in some servers whereby we already had backups by cron jobs ?

Hi,

How long need a recover of all your data, if a disk crashed? 1 hour or 2 hour oder longer? Which priority have your server? Can y have a downtime?

Think about the questions.

With some raid controllers, performance is better in high read rate to write rate environments.

Mirroring keeps your server alive when a disk fails.
Backups keep your company alive in case of a disaster.

With backups you can recover from logical errors, maybe a user deleting a business critical file - mirroring cant help you here.

Business critical servers need both: service continuity (mirroring) in case of a disk failure and business continuity (backup) in case you lose the entire server.

Disasters come in two forms: Hardware failures and operator errors.

Mirroring is the ideal backup for hardware failures, while tapes are the ideal backup for operator errors.


If a hard drive goes down, the mirrored drive takes over. Often, depending on the hardware, the bad drive can be replaced without taking the system down.

This happened to me at my last job. I got a red light on one of the drives. Called IBM and they sent a new drive overnight, with instuctions to simply remove the old drive, 'wait a minute', and insert the new drive.

The only part that surprised me was that I expected to have to issue some type of console command or something. But, no. A few seconds after the new drive was installed, the lights started blinking like crazy as it copied all the data to make it a good mirror. About an hour later, normal blinking resumed.

The important thing was, users never even knew there was a problem.


Tapes provide historical data.

If someone deletes a file, or does some other equally stupid thing, a mirror is no help since that copy will also be bad.