Raid 1 Q Please

[golfmore]

Am I correct in assuming that a Raid 1 config is only as fast as the slowest drive? Is the purpose of Raid 1 just redundancy? If I backup (image) to another drive, it seems that the Raid 1 woouldn't be needed, true? Thanks..

(Haven't been able to get to the chat on Wed. Wife has chemo every week and she's typically out of it for a day or two.)

[kelly]

Don't know about speed. RAID 1 creates an image so you always have 2 identical drives.
- Pros is that if you lose a drive, you can be up-and-running very quickly.
- Cons if you accidently mess up a file on one drive, well, you've done it to both drives. So if you erase some information in for example inside a financial spreadsheet, your backup now has the same erased information.

I've been situations where a database has been messed up and had to retrieve the file from an earlier backup. (I used Retrosect).

So consider what your requirements are when deciding on a backup strategy.

- tony

[dbarrow]

Raid 0 = striped, spans 2 drives
Raid 1 = redundant, copied to 2nd drive
Raid 0+1 = striped, spans 4 drives, carries enough redundant info to rebuild

Big push in the last few years with all the mobo makers offering Raid arrays.
If you hunt down and read the Intel white paper about Intel Application Raid accelerator, it explains all about the burst technology and controller chip and how the drives perform faster with much more data flow at a faster rate... yada, yada ...
The numbers will convince you that Intel Raid in an 0 or 0+1 config is so much faster and superior.

But... in all practicality, with todays fast SATA drives w/ 8mg cache and all the other improvements that have been made in drive technology,
do you actually see/feel the difference? When the bench marks are in ms, does a 100th of a second really make all that much difference? Not that I can notice on a fast machine that has been configured both ways...

Yes, I fell prey to the Raid thing for several years.
It's there so why not use it?
Take two big drives, span them with an array, divide them up into partitions... good to go.

A. 0+1 crash failed to rebuild. Should have but didn't
I carried the 0+1 array with 4 drives on that machine for several years and the one time I counted on it for a fix, it didn't.
B. Most backup/image software has difficulty with Raid
Even though Acronis versions are now touting support for many different Raid configurations, which previously was SOL, I always ran into some form of difficulty in creating or restoring images without some major malfunction or the boot cd wouldn't boot or work right.
C. Frequently see errors in the Event Log where disk controller failed to respond fast enough or some other disk error for Raid array. Not critical enough to cause a crash (yet) but enough to log an error.

My break from Raid came with crash on daughter's machine. I had a good fresh image of the OS completed just prior. It verified. Boot cd brought it up, saw everything, ran a restore and completed.
It wrote everything to one of the two drives on the array instead of spanning, crashed the array and the image file along with it.
The only choice left was to format and restore from Ntbackup (old) alternative backup files, and, being highly PO'd, I dumped the raid and went to 2 SATA individual drives.
I see no performance difference whatsoever.

Given my problems I have encountered with Raid on three machines, I think I'm done with it and, if I ever get around to it, I'll break down the Raid0 on this machine and revert to straight drives.

Raid arrays in server machines with hot swapable drives and banks of spares has a legitimate purpose and works.
I think in home machines, Raid has just not matured into the same level of reliability and redundancy.
If you rely on any image software for backups and have a good "backup solution" with multiple images in multiple locations, I think you are better off without it despite any benchmarks showing better performance.

[kelly]

Point about RAID 0 and maybe it's alreay been made here is that it's actually only 1/2 as reliable as no RAID. Assume 2 drives with equal reliability. When connected in RAID 0, if either dies, you lose everything. So you have 2 chances of a failure instead of only one.
(Note: I'm no statistical expert, it just makes sense to me)
- tony

[Tortanick]

sounds right to me kelly.

[golfmore]

Thanks for thje help. Prob won't do a RAID thing.