RAID1 is not a back up

EddScott

EddScott

EddScott

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Whats the difference between redundancy and backup?

I've got two 500GBs I was going to put into RAID1. I have a 250 which I was going to put my OS and games onto.

The 500s are to store photos and video files. If one of those drives fails, is it not the case that the files will still be accessable from the functioning drive?
 
Roughly... redundancy keeps a server alive in the event of component hardware failure. Backup keeps the business alive in the event of fire, flood or disaster.
I personally wouldn't implement Raid1 in a non-server environment. It won't protect you from accidental deletions/OS corruption screwing a drive up. PSU blowing or power surge could also affect both drives. Errors will be replicated to both drives also.
I'd have one of your 500Gb drives in the PC, using synctoy, robocopy or similar backing it up to the other 500Gb drive in an external device/location/caddy etc.

My 2¢ ;)
 
Raid involves redundancy* - Redundant Array of Inexpensive Disks (there are variations on the name but that is a simple definition) so it is an availability solution and won't guard against user error e.g. you delete the files. It isn't a proper backup and shouldn't be used in place of one but if a drive fails through a mechanical fault then you have a spare that will hopefully allow you to keep your files. Backup should guard against both user error and hardware failure so I'd still recommend keeping a backup of important files on other media - preferably stored offsite in case of fire/flooding etc.

*nb Raid0 is a bit different because it involves striping and no redundancy whatsoever - it could perhaps more accurately be called Aid0 but it simply gets lumped with Raid because it requires a controller to do it.

//edit bah either me or JayMax should have typed faster, it would have prevented repetition. :p
 
JayMax said:
Roughly... redundancy keeps a server alive in the event of component hardware failure. Backup keeps the business alive in the event of fire, flood or disaster.
I personally wouldn't implement Raid1 in a non-server environment. It won't protect you from accidental deletions/OS corruption screwing a drive up. PSU blowing or power surge could also affect both drives. Errors will be replicated to both drives also.
I'd have one of your 500Gb drives in the PC, using synctoy, robocopy or similar backing it up to the other 500Gb drive in an external device/location/caddy etc.

My 2¢ ;)
Click to expand...

Right oh,

So say I still keep the 250 for game and OS and one 500 internally as storage BUT buy an external caddie of some sort to house the other 500 and have some sort of software to back up the internal 500

Any recommendations on an external caddie? drives are SATA

Thanks
 
I do have one [rhetorical] question though - when was the last time you experienced a file system failure on a drive not hosting the OS e.g. NTFS or Ext3 with journalling?

I used a RAID1 of 2 320GB's to house my .pst email file and all my photos. I do have another backup which I do infrequently on DVD-RAM (which is much more resilient that DVD+-R).
 
smids said:
I do have one [rhetorical] question though - when was the last time you experienced a file system failure on a drive not hosting the OS e.g. NTFS or Ext3 with journalling?.
Click to expand...
No that long ago - data corruption on a few video files. 2 mins later they were replaced with copies from the backups.
 
smids said:
I used a RAID1 of 2 320GB's to house my .pst email file and all my photos. I do have another backup which I do infrequently on DVD-RAM (which is much more resilient that DVD+-R).
Click to expand...

This was my way of thinking but I appreciate the risks involved in assuming RAID1 is a backup solution.

Can someone explain these external caddies a bit more. Do I just buy a SATA caddy from OC. Plug it in to the PC and set it to run backups as and when?

With these caddies, they have there own power supply and are not linked to the main drive so errors possible with RAID1 won't occur?
 
There are all sorts of variations of external caddies / drives to suit all requirements. The pre-built ones are pretty much plug in and go, most come with some form of backup software as well but the quality and flexibility of that varies. The self build ones tend to be less sophisticated, pick the caddy to suit the drive and interface you want, slap the drive into the caddy, format the drive if it's new and you're away.

Anything which is based on a 3.5" disk will have an external PSU, 2.5" based caddies will tend to be USB powered, even if they transfer the data using eSATA.
 
rpstewart said:
No that long ago - data corruption on a few video files. 2 mins later they were replaced with copies from the backups.
Click to expand...
Ah, but rp, do you not run a RAID5. Running on a spanned array does increase the chance of corruption does it not? Or is this linked to my lack of knowledge of filesystems and their interactions with physical disk volumes?

I don't dispute any of what you have said, RAID1 is not a backup, however I have always taken the view of needing to appreciate all perspectives.

I don't mean to preach to anyone that RAID1 is a backup, it is clearly not and has always been for redundancy, just so everyone is clear.
 
smids said:
Ah, but rp, do you not run a RAID5. Running on a spanned array does increase the chance of corruption does it not? Or is this linked to my lack of knowledge of filesystems and their interactions with physical disk volumes?
Click to expand...
It may well do, logically there are far more potential failure points in a RAID5 array than a RAID1 one.
 
Can I ask one more question regarding caddies?

Some are internal and some are external. I don't have eSATA so will have to use USB if I get an external caddy. If I get an internal caddie is it still a seperate device? For example if the PSU dies and corrupts the internal HDs will it corrupt the HD in the caddy?
Or is it that the caddy HD only comes to life when backing up?

I guess an internal caddy is still at risk of fire in one location.

Only ask as I don't have much space but I do have a space 5.25 drive bay. Is eSATA faster than USB?
 
I am pretty sure an internal caddie allows you to "eject" the drive out from the caddy (usually on a tray its mounted to) which you could then put in a draw or someplace safe.

I have an Icy Box IB-266STUS-B which you can now get an "internal" caddy for it that fits in to a 3.5" floppy slot (costs an extra £2 with the caddie itself, however ocuk dont stock them). I wish I had got one with the internal bit as its messy having USB (power) + esata cable hanging around at the back of my PC.
 
EddScott said:
Can I ask one more question regarding caddies?

Some are internal and some are external. I don't have eSATA so will have to use USB if I get an external caddy. If I get an internal caddie is it still a seperate device? For example if the PSU dies and corrupts the internal HDs will it corrupt the HD in the caddy?
Or is it that the caddy HD only comes to life when backing up?

I guess an internal caddy is still at risk of fire in one location.

Only ask as I don't have much space but I do have a space 5.25 drive bay. Is eSATA faster than USB?
Click to expand...

Most (if not all) of the eSATA capable IcyBox and IcyDock caddies come with a PCI bracket which routes an internal SATA port to the outside world, this solution works fine for me. OCUK do an Akasa bracket on it's own if you need it but it was out of stock earlier in the week.

eSATA is significantly faster than USB for large files, for smaller ones the difference isn't as marked since the drive spends more time jumping between the MFT and the data so the interface doesn't get saturated.

If a drive is in an internal caddy then it will be powered up and spinning so can be affected by anything which can affect an internal drive. The solution is, as fobose mentions, to remove the drive when it's not in use.
 
For standard home use, external caddies are probably the better option.

The only thing an internal backup protects you against is user-error and drive failure.

An external does those with plus:

1) With a seperate power supply, there is no risk that a catastrophic PSU failure (i.e. BANG!) could damage both the main drive and external drive.

2) If your house is broken into and your PC stolen, there is a reasonable chance the tea-leaf won't bother stealing all the attached peripherals (especially not boring looking grey boxes)

3) If you are going away on holiday it's easier to take the external drive and put it somewhere safe (e.g. neighbours house) so that if your house burns down you won't lose everything.

Backup speed may be lower, but in most cases this isn't something that will cause a real problem.
 
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