RAID 5 Drive Advice

[ScorcherDarkly]

I'm planning to build a RAID 5 array 2-3 TB in size using 1TB drives. Are WD Caviar Blacks still an ok option to use for this? In my research I saw some opinions that WD drives that weren't raid edition weren't useable in raid anymore. I doubt this is the case, but I thought I'd ask people I trust. Also, are there other drives that are more cost effective, or just plan effective, than the Blacks?

Thanks for the help.

 

[FishAk]

You heard correctly about the consumer WD Blacks. Read up on TLER if you need more info, but If you must use WD in RAID, you must use an expensive card that negates TLER, or you must buy the RE models.

The Samsung F3 is a better drive for less money anyway, according to this report. Also, no issue with RAID that I've heard of.

Personally, I would spring fore one more drive, and go with RAID 10. I've seen too many horror stories with RAID 5. In any case, make sure to have a proper backup if you use a RAID array.

 

[Mark R]

You haven't said how you are going to be achieving RAID (hardware card - if so, which card?, motherboard, software) - and with what OS.

The WD (non-RAID edition) drives have a couple of firmware quirks (not so much TLER, but some other slightly odd behavior - aparently something to do with power saving and/or internal self-testing) that gives them a tendancy to fail out of RAID arrays. The RE drives have firmware specifically tuned to avoid this (as well as having TLER).

TLER is an issue with high-end expensive hardware cards - a failing drive can cause severe performance issues if it doesn't have TLER - so high end cards will boot failing non-TLER drives very quickly. TLER drives may stay online in the event of minor damage (a few bad or weak sectors).

Most software RAID doesn't care about TLER (and therefore most consumer level drives should work OK - although RAID edition drives may give slightly better performance in some circumstances due to different cache tuning, etc.). Drives will stay online unless they need to be booted out for data integrity reasons - most software doesn't care much for the performance issue.

I use Seagate LP 1.5 TB drives in linux software RAID, and they work great.

 

[ScorcherDarkly]

Yeah, I had read that TLER was the problem, but wasn't sure if that was just people talking out their butt or not. Thanks for the article. I'll check that out.

What do I get out of RAID 10 versus 5? What kind of problems are there with RAID 5 that are avoided with RAID 10?

 

[RebateMonger]

You might also take a look at alternative ways of creating large volumes out of multiple disks.

MS' Windows Home Server can handle a large number of disks of any size and any type, with no need for a RAID controller or RAID software or special "RAID" disks. If you want, you can enable folder-level disk redundancy, but since you may want backups anyway, you might want to skip the redundancy and make backups.

Note that unless you use GPT partitioning in Windows, you won't be able to use a single virtual disk larger than 2 TB in RAID. WHS gets around this by hiding the individual disks and creating data shares that can be very large.

There are some Linux-based alternatives, too, that can merge multiple disks into one virtual disk.

 

[ScorcherDarkly]

This will be Win7 64 bit, running off the mobo (evga p55 SLI) if at all possible.

 

[FishAk]

What do I get out of RAID 10 versus 5? What kind of problems are there with RAID 5 that are avoided with RAID 10?

You might check out this thread, but basically, unless you use a $400+ card, you swap speed and reliability for some capacity.

 

[ScorcherDarkly]

Is RAID 0+1 the same as RAID 10? Just different notation?

Edit: I see now they are not the same. I will have to investigate further, as my mobo says it supports 0+1, but nothing about 1+0. Hmmm.

 

[FishAk]

No.

RAID 10 is a stripe of mirrors, and RAID 01 is a mirror of stripes. They both perform about the same as RAID 0, and both can survive any single disk loss.

It is the second disk loss that makes the difference. The chance that a RAID 10 array can survive a second disk loss is 66 percent, while for RAID 01 the chance of survival is 33 percent.

Check this link for more info.

Note that Intel says their RST driver (ICH10R) supports RAID 10, but when you create the array, it's called RAID 01, so I don't know which it actually is.