TECH Bye Bye RAID 5 in 2009

1999TL

New Member
Sep 22, 2006
481
Lubbock, TX
Im pondering if I should use raid or not in my new rig i'm about to build. debate lingers on with myself. Drives are just so big now.
 

White Stormy

Take that, subspace!
Sep 17, 2002
85,544
Sparkopolis
Im pondering if I should use raid or not in my new rig i'm about to build. debate lingers on with myself. Drives are just so big now.

just buy two 1TB+ drives and do raid 1. If a drive DID fail, you have a backup.. and if the backup has a read error and fails.. you're no worse off than if you DIDN'T have a backup solution, except you're out an extra $100-150.

if the backup saves you.. it's probably worth more than $100-150, and that's more likely, so sounds to me like it's still the best answer
 
TS
TS

Peyomp

New Member
Jan 11, 2002
13,906
Nothing wrong with using RAID 5 on a 3 disk home array or something, with 1TB disks. His point is that we are fast approaching the point that if an entire disk fails, then you will be quite likely to experience a read error during rebuild. Disks are getting bigger, but failure rates are not getting better.
 

trouphaz

New Member
Sep 22, 2003
2,647
yeah, so what home user is using a 6+1 RAID5 parity group? i wouldn't trust home drives to that little protection. at most i'd go 3+1... though i wouldn't use RAID5 for home anyway. hard drives are cheap and RAID1 (or even RAID1+0) is much better. i can't imagine the rebuild times on many of these low end controllers would be all that great.
 

deusexaethera

OT Supporter
Jan 27, 2005
18,592
This is horseshit. The statistical URE rate might be one bit per 12 terabytes, but that's PER DISK, not for the whole array. In a seven-2TB-disk array with six disks operating simultaneously, you're talking about a URE rate of 1 bit per 72TB, not 12TB.

Anyway, nobody but nobody needs 72TB of data storage, not within reason anyway. Maybe a datacenter has that much capacity, but a datacenter is also going to have far better redundancy than a home user (or even a small office like mine) anyway. We have 4TB of storage and it's half-full -- after five years of continuous operations using data files >1GB apiece, and never deleting anything.

This is nothing more than panic-mongering.
 
TS
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Peyomp

New Member
Jan 11, 2002
13,906
This is horseshit. The statistical URE rate might be one bit per 12 terabytes, but that's PER DISK, not for the whole array. In a seven-2TB-disk array with six disks operating simultaneously, you're talking about a URE rate of 1 bit per 72TB, not 12TB.

This is interesting. What makes you think the rate wouldn't hold across disks? Wouldn't you expect that if you had 1,000,000,000,000 disks, and read 1 byte off each that you would get one bad read?
 

deusexaethera

OT Supporter
Jan 27, 2005
18,592
I say that because while the average number of reads between failures is 12TB, that doesn't mean that the likelihood of failure is identical from Read #1 to Read #n. The MTBF only means that after reading 12TB of data, you have a 50% chance of having suffered one URE; the actual likelihood of failure at any given point in time is described by a hyperbolic curve that starts at 0% at Read #1, crosses the 50% mark at Read #12billion, and trends towards 100% as it approaches Read #Infinity.

Why does that matter? Because if the likelihood of failure per disk starts out infinitesimal and increases as time and wear increase, then that means that 6 disks reading 2TB of data each will not progress as far along the failure-probability curve as a single disk reading 12TB of data would -- the wear is split across multiple disks, so each disk suffers substantially less wear during the rebuild than a single disk would if it had read the same amount of data all by itself. Likewise, the failure-probabilities for all of the drives added together will not equal the failure-probability of a single drive that had read the same amount of data all by itself.
 
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trouphaz

New Member
Sep 22, 2003
2,647
All the Robins I've met were women. Is there a pic of the author anywhere?

20070306_robin1.jpg

Here is a Robin that is a man. It is this guy's son.

alan-thicke-1-sized.jpg
 

deusexaethera

OT Supporter
Jan 27, 2005
18,592
I think we might be getting a little off track.

Good point about Robin Williams though, I forgot about him.
 

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