Why You Need to Backup RAID Arrays

I never trust a single hard drive with anything.  All of my important business systems use RAID, mirroring, and sometimes even replication to protect against common hard drive failures.  Every hard drive is going to fail.  Even solid state drives are not immune to failure.  In fact, I am not yet convinced that SSDs are any more reliable than traditional spinning hard drives.  None of this keeps me awake at night.  Any hard drive can fail and I don't lose a bit of data.  Even with this protection, I still backup all important data because there are other failure scenarios that RAID, and mirroring, and replication don't help with.

We had a database server with high-end HP RAID system attached.  There were two physical arrays, one for the database, and one for the logs.  Each array was RAID AVG (AKA RAID 6), which allows up to two hard drives to fail simultaneously without losing any data.  In addition the arrays had hot spare drives that are activated if any drive fails.  We were also using the highest quality enterprise SCSI drives.  Sounds like we had it covered, right?

That database server went down when the RAID controller failed.  We had no access to any of the data, even though every drive was still healthy.  We couldn't afford to let the server stay offline for a day while a new controller was shipped in. In fact, no controller was going to arrive for a few days because of a snow storm.  Fortunately, we had the data backed up and it was easily restored to an alternate database server.

The loss of a RAID controller is an obvious problem that can occur and common RAID redundancy is going to be of little help.  There are many other scenarios where a good back is the only solution.  RAID, mirroring and replication definitely reduces the stress associated with a disk failure in a critical system, but it is by no means a substitute for effective and reliable backups..

4 comments:

Mike Mavilia said...

I feel you have written right,Jazar. Trusting hard drive is really very hard. You never know, what will happen to it next. So this Backup RAID Arrays can be a good solution to it indeed.

virtual data room said...

There were two physical arrays, one for the database, and one for the logs, which allows up to two hard drives to fail simultaneously without losing any data.

Jared Palmer said...

I've been telling people online for years that RAID is not the same as having a backup, regardless of how much redundancy is in force. I run a data recovery company and constantly see RAID cases come in for recovery. Just this week I quoted the highest price ever for a case (almost $100K!). Customer had a 16 drive RAID 5 EMC SAN which was mirrored onto another EMC SAN hourly. They thought that was a pretty good "backup", until a disgruntled empoyee went and deleted the network share. A few hours later when they noticed, the mirroring had already happened.

There is just no substitute for an offline versioned backup solution.

jazar said...

Great comment Jared! Thanks for reminding all of us. Now with wannacry, cryptolocker and crap going on, offline versioned backups are more important that ever. If you get hit with ransomwear or some other kind of destructive malware, RAID or replication offers no protection.