RAID 5 with Serial ATA 3.0

[davidst99]

Hi, I would like to put 3x 2TB in a RAID 5 configuration. I have 2 Serial ATA 6.0 that I'm using for my SSD drives. Will putting the raid on Serial ATA 3.0 affect performance? Thank you.

David

 

[dave_the_nerd]

Nah, that'd be fine.

Arguably, you shouldn't be using RAID-5, but that's a whole 'nuther issue. (And you'll probably never run into the potential issues.)

 

[davidst99]

Thanks for the reply. What is the downside of using RAID 5? Thanks.

David

 

[dave_the_nerd]

Something called the RAID-5 write hole (potential data loss.)

There are also potential issues with rebuilding arrays that have larger-capacity disks. (If there's a read error during the rebuild, your entire array go boom, no data. The bigger the disks, the more likely a read error is - and 2TB drives are plenty big enough for that to be a concern.)

Storage vendors usually recommend 2x parity drives (RAID-6) for disks 1TB and up, because of the latter issue.

You'd probably be fine. The professionally paranoid among us would suggest you have your RAID array backed up somewhere else as well.

 

[MarkLuvsCS]

^^

well put dave

 

[davidst99]

Thanks for the info. I'll take to a second look at the risks and benefits. I do backup all my files on a NAS drive.

David

 

[smitbret]

Thanks for the info. I'll take to a second look at the risks and benefits. I do backup all my files on a NAS drive.

David

While I wouldn't use RAID 5 in a high I/O environment like a corporate data server, it's fine for home use. It's about perspective. You could get the impression that your Honda Accord is a piece of crap compared to a Lexus when in reality the Accord is exactly what you need.

If you have a decent backup system in place then there's literally no need for anything less efficient. Most likely, you'll never need the backup anyway.

 

[Cerb]

Even in a low-IO environment, it's bad business practice to use RAID 5 (with regular high-density low-URE SATA drives). Not using it has little to with IOPS (RAID 6 is every bit as bad about that, but is standard practice where RAID 5 used to be used), and mostly to do with the write hole and UREs (especially with regular SATA drives). For home use, it should be fine, to give you one drive's worth of warning (though, for few drives, RAID 10 would be better in ever way but cost).

If a drive does fail, just don't trust that the RAID will recover successfully if you replace it. RAID 5 an allow a drive to fail, leaving you with basically a RAID 0 of n-1 drives. In optimum health, it can, with scrubbing, find and correct most UREs, using parity. You have a better chance of retrieving that data from the degraded RAID 5, and then building a new array with that data, than of rebuilding the array with a new drive, and then retrieving that data.

6Gbps v. 3Gpbs means nothing for HDDs, these days.

 

[smitbret]

Even in a low-IO environment, it's bad business practice to use RAID 5 (with regular high-density low-URE SATA drives). Not using it has little to with IOPS (RAID 6 is every bit as bad about that, but is standard practice where RAID 5 used to be used), and mostly to do with the write hole and UREs (especially with regular SATA drives). For home use, it should be fine, to give you one drive's worth of warning (though, for few drives, RAID 10 would be better in ever way but cost).

If a drive does fail, just don't trust that the RAID will recover successfully if you replace it. RAID 5 an allow a drive to fail, leaving you with basically a RAID 0 of n-1 drives. In optimum health, it can, with scrubbing, find and correct most UREs, using parity. You have a better chance of retrieving that data from the degraded RAID 5, and then building a new array with that data, than of rebuilding the array with a new drive, and then retrieving that data.

6Gbps v. 3Gpbs means nothing for HDDs, these days.

High I/O does matter because it increases the chance of failure.

Since RAID is NOT a backup, complete failure of the array in a home environment shouldn't be a big issue. Simply replace the bad hardware and if the parity rebuild fails, just restore from backup.

In any case, most rebuilds from a RAID 5 go just fine. Granted, I've only ever had to do 1 rebuild due to hardware failure (and that was a few years ago before 1TB platters) but I have voluntarily broken up and rebuilt RAID 5 arrays on many occasions and they always work fine.

For home use, most RAID 5 setups won't fail. When they do fail, it's far more common that a simple replace and rebuild repairs it. If that fails it is not catastrophic. Worst case scenario is that the data is unavailable until someone finds 30 minutes to an hour to administer the rebuilds and most of the time is just waiting for tasks to complete and for data to be restored from backup. If my daughter can't watch Dora the Explorer on her iPad for a day she'll survive.