Conflicting advice on backups

I take issue with an article about backups in PC Magazine

Just as patients have to trust their doctors, non-techies have to trust the advice they get from techies. My last posting was about an article in a newspaper that offered, what I felt, was questionable advice on setting up a WiFi wireless network. The July issue of PC Magazine recently arrived in my mailbox and it offers some advice on backing up your computer that is also, to me, questionable.

The article is called "Keep Your Data Safe" and doesn't seem to have been posted yet on pcmag.com.

One section of the article discusses external hard drives (page 72), an excellent medium for storing backup files. The sub-topic on "Multidrives" is what prompted this posting. The magazine defines products in this category as external hard drives that internally contain multiple hard disks (separate and distinct from Network Attached Storage).

RAID 0

One of the products is said to "...hold a pair of 1TB drives for a total of 2TB in a RAID 0 configuration or 1TB of RAID 1 storage.." Another product "uses two 2.5 inch hard drives that are internally connected to get you 500GB of speedy RAID 0 storage."

The term "RAID 0" does not belong in an article about backing up files.

Any hard disk can and will fail. Storing files on a hard disk without backup is playing Russian roulette with your data. You probably knew that. Storing files on a RAID 0 device is playing Russian roulette with two or three bullets in the chamber instead of only one.

RAID 0 is designed for speed. Simply stated, it puts half of each file on each hard disk. It does this because hard disks are brutally slow compared to the CPU and RAM so being able to read from two hard disks at the same time to get a file speeds things up. Fine.

But RAID 0 offers this speed at the cost of reliability. You are more than twice as likely to lose data with RAID 0 as opposed to a single hard disk. For starters, if either hard disk fails, you're facing a data loss. In addition, you may lose everything if the RAID 0 controller fails. A controller may fail in a regular hard disk too, but the RAID 0 controller is keeping track of which half of each file is where. Reconstructing data after a RAID 0 controller failure is likely to require serious expertise and cost thousands of dollars.

To me, suggesting the use of RAID 0 in article about backup is a serious mistake.

A RAID Controller Adaptec

RAID 1

As an earlier quote illustrated, the article also talked about "multdrives" using RAID 1. While RAID 1 is designed for reliability, it's a bit out of place in an external hard disk. RAID 1, presents a single hard disk image to the outside world, but internally it uses two hard disks each one an exact mirror of the other.

The protection offered by RAID 1 however is limited. It doesn't help if you accidentally delete a file or logically corrupt it (where's that missing section from that report?). It doesn't protect you from file system errors such as lost clusters and the like. And it introduces the RAID controller as something else that can fail and isn't cheap. Finally, external hard disks are usually sealed, so if one hard disk in a RAID 1 configuration fails, the protection it offered is gone for good.

RAID 1 makes sense in servers that need high availability, such as those running this very website. It also makes sense in a NAS (Network Attached Storage) device where you can replace a failed hard disk easily. But, for external hard disks used for backup, you are safer with two independent devices as opposed to a single device running RAID Level 1. It may even be cheaper.

Western Digital's Raptors in RAID-0: Are two drives better than one? at anandtech.com (July 2004) offers a good introduction to RAID Level Zero and Level One. It also reports on seven different speed tests of RAID 0. The conclusion? Quoting "...there is no place, and no need for a RAID-0 array on a desktop computer. The real world performance increases are negligible at best and the reduction in reliability, thanks to a halving of the mean time between failure, makes RAID-0 far from worth it on the desktop."

My first real posting on this blog was about RAID Level Zero, see Don't get burned by RAID Zero and Following up on RAID Level Zero .

See a summary of all my Defensive Computing postings.

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About the author

    Michael Horowitz wrote his first computer program in 1973 and has been a computer nerd ever since. He spent more than 20 years working in an IBM mainframe (MVS) environment. He has worked in the research and development group of a large Wall Street financial company, and has been a technical writer for a mainframe software company.

    He teaches a large range of self-developed classes, the underlying theme being Defensive Computing. Michael is an independent computer consultant, working with small businesses and the self-employed. He can be heard weekly on The Personal Computer Show on WBAI.

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