RAID5 vs RAID6

aerospyke · 8th January 2009, 11:34 AM

Hey all,

I have a RAID controller that can do both RAID 5 AND RAID6 ... Is it just a given that I may prefer RAID6?

Bangers · 8th January 2009, 11:43 AM

If it's a given if the likelihood of having a second drive fail during the rebuild process of the original drive.

It's simple maths of rebuild time versus MTTF. You can also factor in controller smarts in relation to how quickly they can detect a failure and kick in a hotspare. This is how enterprise Storage RG's can get away with running 5D+1P RAID5 with per shelf HP's because once they notice a drive error, it's very quick for them to rebuild the array not only from base disk data but also from controller cache. Not to mention the much more reliable drives they also use.

aerospyke · 8th January 2009, 12:13 PM

Fair crack.... well the card I have is

http://www.lsi.com/storage_home/prod...elp/index.html

I have not hte drives yet, as I am waiting for the 7200.12 drives (500GB..ish platters FTW) and getting the enterprise drives. It is a home server but it will be 24/7 (not to mention its also my sandpit area for my work experiments) so i want it to last.... oh they are going to be 4x (or 5 depending on all other things) 1.5TB drives, so rebuild time is prolly gunna be a killer!

saba · 8th January 2009, 12:52 PM

RAID-6 starts to make sense as the number of devices in an array starts to climb above six or seven.

jmeister · 8th January 2009, 12:55 PM

4 x 1.5tb drives in RAID 6?

my LSI 84016E does not let me configure raid6 when I only have 4 drives in the array.

aerospyke · 8th January 2009, 12:59 PM

Quote:

Originally Posted by saba

RAID-6 starts to make sense as the number of devices in an array starts to climb above six or seven.

so being a 4-5 device array, RAID 6 has no TRUE benefits over RAID5 other than the resistance of an extra drive failure taking the array down?

Sadow · 8th January 2009, 1:04 PM

Quote:

Originally Posted by aerospyke

so being a 4-5 device array, RAID 6 has no TRUE benefits over RAID5 other than the resistance of an extra drive failure taking the array down?

Why are you set on raid 5 or raid 6? drives are so cheap, much better and safer to run raid 10

aerospyke · 8th January 2009, 1:28 PM

I'm not really "set" per-se on RAID 5 or 6, rather just prefer it as i lose less space than in RAID 10. I do understand the advantages of 1+0 over 5.

jmeister · 8th January 2009, 3:29 PM

I think the best solution for most people is what I have setup recently.

a RAID 0+1 for critical drives and a RAID 5 for mass storage of non-critical data.

this way you lose less capacity while maintaining redundancy for the important things anyway

aerospyke · 8th January 2009, 4:25 PM

Quote:

Originally Posted by jmeister

I think the best solution for most people is what I have setup recently.

a RAID 0+1 for critical drives and a RAID 5 for mass storage of non-critical data.

this way you lose less capacity while maintaining redundancy for the important things anyway

that is what I have for my current physical servers... this is for storage in a VMware environment (yes I wil have ESXi running at home

) for storage of my VMDKs for OS's and data

hapkido · 9th January 2009, 12:15 AM

Quote:

Originally Posted by aerospyke

I'm not really "set" per-se on RAID 5 or 6, rather just prefer it as i lose less space than in RAID 10. I do understand the advantages of 1+0 over 5.

Ummm, This is incorrect.
Although RAID 10 offers higher a higher degree of protection than RAID 5, it does not come close to RAID 6.

RAID 6 offers protection in the event that any two disks fail. RAID 10 does NOT offer protection if 1 drive in each mirror fails. Work it out computationally if you like.

hapkido · 9th January 2009, 12:29 AM

Quote:

Originally Posted by jmeister

4 x 1.5tb drives in RAID 6?

my LSI 84016E does not let me configure raid6 when I only have 4 drives in the array.

So in this case, if RAID 6 was an option you would still get the same useable as if you were to use RAID 10. RAID 10 = fast but poor utilisation (as in 50%).

As mentioned in my previous post RAID 6 offers the best protection of any RAID configuration available. The tradeoff is that it is also the slowest. The reason for this is that RAID 6 has to complete two different parity calculations and creates more read/writes than RAID 5 (which is only a single parity calculation). If you want understand the differences in more detail, go here:
http://en.wikipedia.org/wiki/Redunda...ependent_disks

The fact that you are using SATA drives and not 15K SAS/FC/SCSI drives says 'performance' is not your critical aim. Depending on the use of your system, it is possible or even likely that RAID 6 (with more drives) will be acceptabe performance.

Sadow · 9th January 2009, 12:33 AM

Quote:

Originally Posted by hapkido

Ummm, This is incorrect.
Although RAID 10 offers higher a higher degree of protection than RAID 5, it does not come close to RAID 6.

RAID 6 offers protection in the event that any two disks fail. RAID 10 does NOT offer protection if 1 drive in each mirror fails. Work it out computationally if you like.

would have the be corresponding drives in each mirror, which becomes less likely the bigger the arrays.

Write performance still takes a big hit with raid 6, and recovery time is still much larger than with a raid 10 array.

hapkido · 9th January 2009, 12:54 AM

Sorry Sadow and aerospyke.

I quoted the incorrect sentance.

It was meant to be

"Why are you set on raid 5 or raid 6? drives are so cheap, much better and safer to run raid 10".

It was simply in reply to 'safer' which indeed RAID 10 is not. But yes certainly faster.

oli · 9th January 2009, 12:57 AM

Personally I'd only bother with RAID6 if I was running an array with over 5 or 6 drives. Any less and RAID5 is OK.

8th January 2009, 11:34 AM	#1
aerospyke Member Join Date: Aug 2005 Location: Sydney NSW Posts: 3,180	RAID5 vs RAID6 Hey all, I have a RAID controller that can do both RAID 5 AND RAID6 ... Is it just a given that I may prefer RAID6? __________________ DFI Lanparty UT nf4 SLI-DR Expert BIOS 0406 \| G4 on AMD 4400+@2.7Ghz (270x10) \| G.Skill HZ 2GB@1:1 \| MCW55 on 7800GTX 256 @ 500/1.39 Wife v1.2 settling in fine, no compatibility issues apparent ZOMG bought myself a house !

8th January 2009, 11:43 AM	#2
Bangers Member Join Date: Dec 2001 Location: Silicon Valley Posts: 7,281	If it's a given if the likelihood of having a second drive fail during the rebuild process of the original drive. It's simple maths of rebuild time versus MTTF. You can also factor in controller smarts in relation to how quickly they can detect a failure and kick in a hotspare. This is how enterprise Storage RG's can get away with running 5D+1P RAID5 with per shelf HP's because once they notice a drive error, it's very quick for them to rebuild the array not only from base disk data but also from controller cache. Not to mention the much more reliable drives they also use. __________________ There's a story about a golfer who sinks a 30-meter putt and someone says: 'Gee, that was lucky' and the golfer says, 'Yes, amazing how lucky you get when you practice 8 hours a day for 20 years'.

8th January 2009, 12:13 PM	#3
aerospyke Member Join Date: Aug 2005 Location: Sydney NSW Posts: 3,180	Fair crack.... well the card I have is http://www.lsi.com/storage_home/prod...elp/index.html I have not hte drives yet, as I am waiting for the 7200.12 drives (500GB..ish platters FTW) and getting the enterprise drives. It is a home server but it will be 24/7 (not to mention its also my sandpit area for my work experiments) so i want it to last.... oh they are going to be 4x (or 5 depending on all other things) 1.5TB drives, so rebuild time is prolly gunna be a killer! __________________ DFI Lanparty UT nf4 SLI-DR Expert BIOS 0406 \| G4 on AMD 4400+@2.7Ghz (270x10) \| G.Skill HZ 2GB@1:1 \| MCW55 on 7800GTX 256 @ 500/1.39 Wife v1.2 settling in fine, no compatibility issues apparent ZOMG bought myself a house !

8th January 2009, 12:52 PM	#4
saba Evil Vizier Join Date: Aug 2001 Location: Melbourne Posts: 2,711	RAID-6 starts to make sense as the number of devices in an array starts to climb above six or seven. __________________ i7 920 ; Asus P6T Deluxe ; 12Gb DDR3-1333 ; nVidia 260 GTX powering 230" LCDs ; 315k SAS RAID-0 and 5*1.5TB WD EARS RAID-5 on a Adaptec 5805 ; Windows 2008 Server and Gentoo Linux ; RME Fireface 800 56-channel 24bit/192kHz soundcard

8th January 2009, 12:55 PM	#5
jmeister Member Join Date: Aug 2006 Location: Sydney Posts: 142	4 x 1.5tb drives in RAID 6? my LSI 84016E does not let me configure raid6 when I only have 4 drives in the array. __________________ Main: i7 2700 \| 32GB \| PowerColor 6970 \| Sidewinder X8 \| 120GB Intel 520 \| 2 x Dell 24" Fileserver: i7-950 \| 24GB \| Corsair HX-1000 \| Norco 2442 \| Logitech G7 Carbon \| 44TB \| LSI 9260 + Chenbro SAS Expander + 3ware 9690SA \| Server 2008 R2 Over $5000+ in trades.

8th January 2009, 1:28 PM	#8
aerospyke Member Join Date: Aug 2005 Location: Sydney NSW Posts: 3,180	I'm not really "set" per-se on RAID 5 or 6, rather just prefer it as i lose less space than in RAID 10. I do understand the advantages of 1+0 over 5. __________________ DFI Lanparty UT nf4 SLI-DR Expert BIOS 0406 \| G4 on AMD 4400+@2.7Ghz (270x10) \| G.Skill HZ 2GB@1:1 \| MCW55 on 7800GTX 256 @ 500/1.39 Wife v1.2 settling in fine, no compatibility issues apparent ZOMG bought myself a house !

8th January 2009, 3:29 PM	#9
jmeister Member Join Date: Aug 2006 Location: Sydney Posts: 142	I think the best solution for most people is what I have setup recently. a RAID 0+1 for critical drives and a RAID 5 for mass storage of non-critical data. this way you lose less capacity while maintaining redundancy for the important things anyway __________________ Main: i7 2700 \| 32GB \| PowerColor 6970 \| Sidewinder X8 \| 120GB Intel 520 \| 2 x Dell 24" Fileserver: i7-950 \| 24GB \| Corsair HX-1000 \| Norco 2442 \| Logitech G7 Carbon \| 44TB \| LSI 9260 + Chenbro SAS Expander + 3ware 9690SA \| Server 2008 R2 Over $5000+ in trades.

9th January 2009, 12:54 AM	#14
hapkido Member Join Date: Sep 2003 Location: Brisbane Posts: 291	Sorry Sadow and aerospyke. I quoted the incorrect sentance. It was meant to be "Why are you set on raid 5 or raid 6? drives are so cheap, much better and safer to run raid 10". It was simply in reply to 'safer' which indeed RAID 10 is not. But yes certainly faster.

9th January 2009, 12:57 AM	#15
oli Member Join Date: Jun 2002 Location: The Internet Posts: 7,175	Personally I'd only bother with RAID6 if I was running an array with over 5 or 6 drives. Any less and RAID5 is OK.