Great article.
Should be a useful resource for pointing people to if they want assistance with RAID for whatever reason.
One thing I was confused about was only two disks in raid1?
I could've sworn you could have more.
Though I assume it would act like JBOD+1,
ie, two disks in a mirror, then another two in a mirror, then JBOD the two together?
I may try to find the article I read previously to see if it says differently. :)
Quote:
There is also a chance of data loss due to physical drive defects, such as bad clusters, as the controller may duplicate the data loss across both of the drives.
Are you sure??
I wouldn't have thought a bad cluster one one disk would cause the other disk to have any problems?
I assume the controller may get a bit confused if it reads from both and gets different results though?
Keep these articles coming, especially the linux ones.
A few more of those and I may just take the plunge... :D
Originally Posted by Glider Great article, but I do miss some examples of RAID implementations (like some good HW cards, Soft vs Hardware RAID [I think Linux here]),...
But nothing is perfect, and there's always something somebody wants added
well, I guess we finally found something we agree on Glider ;)
from my own experience using quite a few cards, 3ware tend to be the best, though Areca are the people to go to for RAID 6; for easily affordable cards, go Promise or Syba (non bootable, usually only 1,0,5 and generally cheap; bootable will cost a bit more)
I personally don't see the point in RAID until you have got enough storage space as the money could be spent on more drives. As one can never have enough storage space there is no need for raid ;)
I always thought (in terms of gaming) RAID was meant to increase load times and that it made a big difference overall, but I guess not. Especially for the price. I wonder if RAID will/can be implemented with these new SSD's coming out soon (not that I would want to spend the $ to try)....
Honestly, I would rather just backup my stuff onto an external HD (which I currently do). Sounds a whole lot safer to me because of power outtages and lightning strikes, hackers, viruses, etc. AND you can take it outside of your house.
Originally Posted by devdevil85 I always thought (in terms of gaming) RAID was meant to increase load times and that it made a big difference overall, but I guess not. Especially for the price. I wonder if RAID will/can be implemented with these new SSD's coming out soon (not that I would want to spend the $ to try)....
I recall reading about some guy that had created a 16GB array using gigabyte's I-RAM drives, which hold 4GB of DDR 400mhz and uses a SATA-II interface, which could then be connected to a RAID card, i fail to find the article, tho here is a link to a video of XP booting of such setup. z0mg fast!!! http://video.google.com/videoplay?docid=-51784544344753709&q=Gigabyte
Originally Posted by r4tch3t Filled me in on a few things, like RAID 3 and 4 and RAID 1 only supporting 2 drives, I thought it could be more, like having two redundant drives.
I'm pretty sure this is one of the biggest mistakes in the article
RAID1 can support 2+ disks, the more discs, the more redundancy, but the increased wasted space (3 drives = 1/3 space available, 4 drives = 1/4 etc)
Quote:
Originally Posted by Wikipedia RAID 1: Mirrored Set (2 disks minimum) without parity: provides fault tolerance from disk errors and single disk failure. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning.
However, the article did clear 1 thing up for me, i thought as raid 5/6 arrays got bigger it could sustain more drive losses, however after reading this article (and thinking it was wrong) i read up on it, and you are indeed right
That kinda sucks as the best fault tolerance with least wasted space is RAID6 (in big arrays) only allows 2 dead discs
P.S. there is a RAID50 mode which is a raid5+0 - which offers better performance then raid 5, plus marginally better fault tolerance http://www.acnc.com/04_01_00.html
i usually look at this website for a raid reference, although bit tech does clear up the fact raid really doesnt help the home user much
Also, one of the biggest misconceptions is that you don't need to backup, i recently accidentally overwrote a file, and nothing could retrieve it (due to it being overwritten and not deleted) which lost me hundreds of hours of work :(
Originally Posted by completemadness I'm pretty sure this is one of the biggest mistakes in the article
RAID1 can support 2+ disks, the more discs, the more redundancy, but the increased wasted space (3 drives = 1/3 space available, 4 drives = 1/4 etc)
I have yet to see a single controller that supports more than 2 disks in RAID1, and I've seen a good few controllers. Using more than two disks in a RAID1 configuration typically means combining it with RAID0
RAID50 is typically slower than RAID6 and is less fault tolerant. Seeing that you're unlikely to ever see it in a desktop environment I opted to leave it out ;)
One thing I was confused about was only two disks in raid1?
I could've sworn you could have more.
Though I assume it would act like JBOD+1,
ie, two disks in a mirror, then another two in a mirror, then JBOD the two together?
I may try to find the article I read previously to see if it says differently.
its called RAID 0+1 you need mini 4 disks
2 sets of 2 hdds
two are stripeing and the other 2 disks are been mirrored as stripeing (i am quite sure he talked about that as you lose Half of the disk space dule to mirroring)
note
Nvidia onboard RAID sucks an little on the speed there is no point in useing more then 2 disks in striping (RAID0) as speed will not go up that much going from 1 disk to 2 disks is alot better
my setup
4x80
2x RAID0 XP on one and Vista on the other and an 500GB driver and norm working files (i not realy bothed to backup the disk as my inportant stuff is stored els where)
Originally Posted by Mister_Tad I have yet to see a single controller that supports more than 2 disks in RAID1, and I've seen a good few controllers. Using more than two disks in a RAID1 configuration typically means combining it with RAID0
Your probably right, but i still think its the wrong thing to write, RAID1 does support more then 2 discs, but controllers need to implement this, just because its in the spec but hardware doesn't do it, doesn't mean the spec has changed
I'm sure some raid controllers do offer >2 disc RAID1 arrays, and for the ultimate fault tolerance, nothing beats it, if you have ultra mission critical data, its the best way to do it
Edit:
Perhaps a small footnote at the end of the raid1 article just saying it does support more then 2 discs, but it is infrequently implemented
RAID1 doesn't support more than one disk. One could technically mirror a disk to more than one other disk, which im sure would require proprietary hardware/software, but it wouldn't strictly be RAID1, it would be 3-way mirroring.
3+way mirroring wouldn't really be the "ultimate" fault tolerance. The reason that it has never been implemented (or certainly never caught on) is that there are more effective ways of providing fault tolerance without such a waste of space: duplexing, off-site mirroring, offsite+online backups, RAID 51, 53, 61 etc.
Originally Posted by leexgx its called RAID 0+1 you need mini 4 disks
2 sets of 2 hdds
two are stripeing and the other 2 disks are been mirrored as stripeing (i am quite sure he talked about that as you lose Half of the disk space dule to mirroring)
I was think JBOD over raid0 so that even if the two disks in one mirror pair failed, you wouldn't lose everything.
Even so, you would still lose some which wouldn't be much use. :/
Nice article maybe could've touched on a bit about JBOD I know it's not technically a RAID solution but almost all consumer RAID controllers offer it and it would've flowed with the "what's best for home use" theme.
The more hard drives you have the more succeptible you are to hard drive failure and thus the more expensive your solution.
Google proved that hard drives fail incosistently, there's no way of detecting an imminent failure to a significant enough extent, there's no specific brand which fails the most, it's just which end users are most vocal about their problems.
"Currently 2.5 15k RPM drives are the crème de la crème of high I/O performane, and youre going to need more than one of them as the largest available is a mere 73GB. "
you sure about that?
cos im writing this with an array of 16 146.8 gig 15K 2.5 RPM sas drives sitting infront of me, in the same place it has done for the last 6 months. :)
Thank you for this article, it quite perfectly explains the most important things you need to know about RAID to understand how it works (adding the details about XOR parity generation has been a good idea)!
It just so happens to be, that i finished building my own RAID-6 array a few days ago. I was using two RAID-5 arrays before, and i started using RAID as soon as it hit the desktop market with levels 0 and 1 in the beginning.
My Controllers so far: Promise FastTrak 66 RAID-0, Intel ICH RAID-0, nVidia nForce4i RAID-0, Promise SuperTrak SX6000 RAID-5 (two array, first with 120GB WD disks, then migrated to 300GB MaxLines), finally a 3Ware 9650SE-8LPML.
I have now switched to 3Ware because there already are Vista Beta Drivers, and Final Drivers to be released soon (and of course because of FAR higher performance, higher fault tolerance, more space and so on).
Current Array:
3Ware 9650SE-8LMPL with Battery Backup Unit 03
8 x Hitachi 7K1000 1TB HDDs
For those who are interested, here are a few Benchmarks and Pics of this array. Read speed is around the 100-160MB/s mark, writes are around the 50MB/s mark (NTFS compression is active). Read scores can be ignored for ATTO Disk Benchmark, as reads were unfortunately cached here..
Master Boot Records only have 32-Bit Addressing and physical drives have 512 byte sectors, that makes a maximum of 2TB for physical drives. So larger arrays have to be split up into smaller <=2TB pieces, that can be put together again by using dynamic discs and a "JBOD" volume in Windows XP:
It is very comfortable to have ALL your data, be it your DVD Movies or Games, be it music or just a whole lot of old files accessible by just a few clicks! I love huge RAID Arrays, oh yes. ;)
Originally Posted by Glider Edvuld, you are talking backups... RAID isn't backup... RAID is protection against Harddrive failure... Safe data is data on redundant array + a good Backup routine.
Thank you. I might have written it in a bad way, but that was exactly what I was trying to point out. Many think that just because you got a RAID1 array set up, you don't need to do backups.
Originally Posted by Edvuld Thank you. I might have written it in a bad way, but that was exactly what I was trying to point out. Many think that just because you got a RAID1 array set up, you don't need to do backups.
but once you start piling up the terrabytes it starts getting hard to backup for less then the array cost you :(
Comments 26 to 46 of 46
Should be a useful resource for pointing people to if they want assistance with RAID for whatever reason.
One thing I was confused about was only two disks in raid1?
I could've sworn you could have more.
Though I assume it would act like JBOD+1,
ie, two disks in a mirror, then another two in a mirror, then JBOD the two together?
I may try to find the article I read previously to see if it says differently. :)
I wouldn't have thought a bad cluster one one disk would cause the other disk to have any problems?
I assume the controller may get a bit confused if it reads from both and gets different results though?
Keep these articles coming, especially the linux ones.
A few more of those and I may just take the plunge... :D
-- Fixed, thanks! - Da Dego
well, I guess we finally found something we agree on Glider ;)
from my own experience using quite a few cards, 3ware tend to be the best, though Areca are the people to go to for RAID 6; for easily affordable cards, go Promise or Syba (non bootable, usually only 1,0,5 and generally cheap; bootable will cost a bit more)
Honestly, I would rather just backup my stuff onto an external HD (which I currently do). Sounds a whole lot safer to me because of power outtages and lightning strikes, hackers, viruses, etc. AND you can take it outside of your house.
I recall reading about some guy that had created a 16GB array using gigabyte's I-RAM drives, which hold 4GB of DDR 400mhz and uses a SATA-II interface, which could then be connected to a RAID card, i fail to find the article, tho here is a link to a video of XP booting of such setup. z0mg fast!!!
http://video.google.com/videoplay?docid=-51784544344753709&q=Gigabyte
RAID1 can support 2+ disks, the more discs, the more redundancy, but the increased wasted space (3 drives = 1/3 space available, 4 drives = 1/4 etc)
That kinda sucks as the best fault tolerance with least wasted space is RAID6 (in big arrays) only allows 2 dead discs
P.S. there is a RAID50 mode which is a raid5+0 - which offers better performance then raid 5, plus marginally better fault tolerance
http://www.acnc.com/04_01_00.html
i usually look at this website for a raid reference, although bit tech does clear up the fact raid really doesnt help the home user much
Also, one of the biggest misconceptions is that you don't need to backup, i recently accidentally overwrote a file, and nothing could retrieve it (due to it being overwritten and not deleted) which lost me hundreds of hours of work :(
I have yet to see a single controller that supports more than 2 disks in RAID1, and I've seen a good few controllers. Using more than two disks in a RAID1 configuration typically means combining it with RAID0
RAID50 is typically slower than RAID6 and is less fault tolerant. Seeing that you're unlikely to ever see it in a desktop environment I opted to leave it out ;)
take a look at casper xp
its called RAID 0+1 you need mini 4 disks
2 sets of 2 hdds
two are stripeing and the other 2 disks are been mirrored as stripeing (i am quite sure he talked about that as you lose Half of the disk space dule to mirroring)
note
Nvidia onboard RAID sucks an little on the speed there is no point in useing more then 2 disks in striping (RAID0) as speed will not go up that much going from 1 disk to 2 disks is alot better
my setup
4x80
2x RAID0 XP on one and Vista on the other and an 500GB driver and norm working files (i not realy bothed to backup the disk as my inportant stuff is stored els where)
I'm sure some raid controllers do offer >2 disc RAID1 arrays, and for the ultimate fault tolerance, nothing beats it, if you have ultra mission critical data, its the best way to do it
Edit:
Perhaps a small footnote at the end of the raid1 article just saying it does support more then 2 discs, but it is infrequently implemented
3+way mirroring wouldn't really be the "ultimate" fault tolerance. The reason that it has never been implemented (or certainly never caught on) is that there are more effective ways of providing fault tolerance without such a waste of space: duplexing, off-site mirroring, offsite+online backups, RAID 51, 53, 61 etc.
Even so, you would still lose some which wouldn't be much use. :/
Google proved that hard drives fail incosistently, there's no way of detecting an imminent failure to a significant enough extent, there's no specific brand which fails the most, it's just which end users are most vocal about their problems.
you sure about that?
cos im writing this with an array of 16 146.8 gig 15K 2.5 RPM sas drives sitting infront of me, in the same place it has done for the last 6 months. :)
It just so happens to be, that i finished building my own RAID-6 array a few days ago. I was using two RAID-5 arrays before, and i started using RAID as soon as it hit the desktop market with levels 0 and 1 in the beginning.
My Controllers so far: Promise FastTrak 66 RAID-0, Intel ICH RAID-0, nVidia nForce4i RAID-0, Promise SuperTrak SX6000 RAID-5 (two array, first with 120GB WD disks, then migrated to 300GB MaxLines), finally a 3Ware 9650SE-8LPML.
I have now switched to 3Ware because there already are Vista Beta Drivers, and Final Drivers to be released soon (and of course because of FAR higher performance, higher fault tolerance, more space and so on).
Current Array:
3Ware 9650SE-8LMPL with Battery Backup Unit 03
8 x Hitachi 7K1000 1TB HDDs
For those who are interested, here are a few Benchmarks and Pics of this array. Read speed is around the 100-160MB/s mark, writes are around the 50MB/s mark (NTFS compression is active). Read scores can be ignored for ATTO Disk Benchmark, as reads were unfortunately cached here..
Master Boot Records only have 32-Bit Addressing and physical drives have 512 byte sectors, that makes a maximum of 2TB for physical drives. So larger arrays have to be split up into smaller <=2TB pieces, that can be put together again by using dynamic discs and a "JBOD" volume in Windows XP:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-dyn.gif
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-size.gif
POST:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-3bm-7.jpg
Cooling by Antec HDCS (2 temp controlled Y.S. Tech Fans, two temp sensors, massive aluminium block):
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-cooling-3.jpg
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-cooling-3.jpg
The whole thing built in:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-builtin-2.jpg
HDTach Quick Bench, 8MB Zones:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-hdtach.gif
HDTach Long Bench, 32MB Zones:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-hdtach-32mb.gif
ATTO Disk Bench:
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-atto1.gif
HD Tune (sorry, got no thumbnail here):
http://www.xin.at/thrawn/pics/hw/3ware-helios-raid6/final/raid6-hdtune.gif
It is very comfortable to have ALL your data, be it your DVD Movies or Games, be it music or just a whole lot of old files accessible by just a few clicks! I love huge RAID Arrays, oh yes. ;)
Thank you. I might have written it in a bad way, but that was exactly what I was trying to point out. Many think that just because you got a RAID1 array set up, you don't need to do backups.