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[joeyjoey]

Hi everyone, I'm a new owner of DNS-321 and although I assumed I would be using RAID when I purchased it, I've suddenly started wondering what the real practical purpose and benefit of RAID would be for an external drive like this.

I understand RAID protects against hardware failure, at least if only a single disk fails.  I understand it does not protect against anything that intentionally rewrites data on your disk (deletion, virus, etc.) as the other disk is just a direct copy.  I also understand that if the controller fails this could leave both disks unreadable (does such a thing happen often?).  Forgive me for not having much understanding of the EXT2 filesystem, but I've had nasty MFT master file table errors in the past and am wondering if this is the type of error that would be copied to both disks, rendering both inaccessible, or it's the type of error that would normally be limited to one disk under RAID.

I got on a bit of a tangent there.  But all questions I'm wondering about.

So, I feel like I must be overlooking something, but the only benefit of RAID-1 that I really see a use for would be fast disk replacement, if someone could not afford any downtime of their system.  For home users, however, who are just using this to store photos and media files etc., downtime really doesn't seem like it should be an issue.  Is there a benefit/s I'm overlooking here???

It seems like if backup is your major concern, and you do not care about downtime, then a RAID setup might actually be worse than just having separate volumes and letting one backup the other periodically.  I'm reasoning that those types of errors that do get instantly copied disk-to-disk in a RAID setup will be avoided by a scheduled backup process.  (Clearly, you might lose any files that have changed since your last backup, but that also seems relatively minor if backups are often performed.)

The ideal backup process, to me, would be one that continually backed up your files, but also always kept track of all changes made the past hour/day/week (whatever your choose).  Something like "RAID with restore points or delayed write" if such a thing exists.

Anyway, the primary question, again, is whether RAID really does have any benefits for someone concerned far more with data backup than downtime.  I've just started questioning this now, right before setting up my 321, but RAID is so popular I feel like I'm missing something.  Actually, I haven't opened the 321 yet, would a single-bay NAS with external backup be a better option?  Thanks so much for any advice.

[fordem]

You're 100% correct - disk redundancy is about reducing downtime, and if you don't care about downtime, then you're better off without it.

[nrf]

While "downtime" is a good term to use in this discussion, there is another parameter which seldom gets mentioned. That parameter relates to "recent data loss". Unless the backup scheme is continuous, loss of a hard disk would result in loss of files/changes that hit the disk since the last backup.

Depending on how much effort you want to place on frequent or continuous backup methods, this might be a motivation for raid too. Evaluating it would involve thinking about how frequently your data changes, what would happen if you lost some of it, etc.

FWIW.
nrf

[fordem]

While "downtime" is a good term to use in this discussion, there is another parameter which seldom gets mentioned. That parameter relates to "recent data loss". Unless the backup scheme is continuous, loss of a hard disk would result in loss of files/changes that hit the disk since the last backup.

Depending on how much effort you want to place on frequent or continuous backup methods, this might be a motivation for raid too. Evaluating it would involve thinking about how frequently your data changes, what would happen if you lost some of it, etc.

FWIW.
nrf

Be that as it may - having a redundant disk array does NOT remove the need for backup, and a RAID array without the frequent or continuous backup methods you suggest will still be subject to the potential for data loss, just not data loss caused by disk failure.

The "raison d'etre" of RAID is to reduce and hopefully eliminate the downtime that results when a disk fails - if downtime is not an issue for consideration then RAID is of little value - why would anyone want to invest in the storage capacity to hold three copies of their data - (two copies for RAID1 + the backup)

[nrf]

You seem to have missed my point, I am not disagreeing with you - I am saying that raid does more than save you recovery time, it can also avoid short-term loss of changes/files that your backup scheme has not yet captured.

If you use nightly backups and have no raid, you can lose a day's work to a disk failure. If you backup every 2 hours you can lose 2 hours of work etc. With raid, you can lose a disk and still have the last so many hours/minutes of data, which may be very valuable to someone.

When establishing a data security plan, it pays to consider what is at risk in each type of failure. For example, you want 'up to the minute' backups so every last changed file gets copied out to a share drive but find that the trojan you picked up wiped that disk too. Or maybe you don't care if you lose 'recent' data, I am suggesting you consider your needs and use the technology mix that suits your situation.

There are a whole spectrum of choices including internet backups, off-site storage, multiple usb drives, etc. but the right mix of hardware and software depends on your needs and deserves careful consideration if one's data is 'valuable' to them.