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What is the difference between striped raid and mirrored raid?
I know it's a pretty basic question, but I'm a noob...we've all been there...The only beans I like are Jelly Beans!!!
I've been reading the forums and wondering the same thing. Here's how I understand it:
In mirrored RAID, the files are written twice, once to each hard drive. That's good for users who want a constant backup of their hard drive.
In striped RAID, the files are split and placed half on each drive. It speeds up file access.
Best Wishes,
Bob
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Striping is when you are writing one set of data too two partitions or two drives. Mirroring is when you are writing the same data too two separate partitons or drives. Striping-RAID 0, Mirroring-RAID 1. There are other combinations of RAID. 5 in all I believe. Striping is usually done to gain drive access speed. Mirroring to protect data.
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Striping is for performance. But if one drive fails you're totally screwed and your data is toast. On the other side of it, mirrorring is like having two exact same drives running same thing. And all that happens is it writes everything twice. It's a security thing, for those whose data is so important they must have a backup if the main drive fails.
Like O'thehill said. But I typed it all out again cause I am a little parrot. PLus I thought I'd let ya know about the risks of striping without backup. My question driectly after yours funnily enough is on the same topic. You might want to read the answer to it, if I get any!
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Very good. Additionally mirroring requires 2 hard drives while striping requires at least 3. With striping a single hard drive can fail and new one can be put in its place to maintain the stripe.
-DF
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Actually he's right RAID 0 striping can use 2 disks and will screw you. RAID 5 striping uses 3 or more and won't screw you. And of course RAID 1 is mirroring.
-DF
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say you have two 80GB drives and 80 1GB files.
If you stripe, half of each file goes onto a separate drive and the transfer speed is about twice as fast since each time you access a file you retrieve it from two concurrently spinning disks. You use up 80GB of 160GB of space. Performance is high and reliability is low.
If you mirror, each entire file goes onto a separate drive and the transfer speed is normal. You use up 80GB of 80B of space. Performance is normal and reliability is high.
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If you mirror your tranfer speed is actually lower than with one drive due to the overhead of the controller. Add to that the ECC memory usually used with such systems and you take another performance hit. This type of box is built for dependability though so speed is not of the essence. Most servers don't run real fast processors anyway.
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Lol, those boys at silicon graphics probably do! I hope so, hurry the bleep up and get Monsters Inc 2 out!!!!
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Not forgetting Sun Microsystems of course. Also listed at the end of Pixar movies... poor Disney, doomed... dooomed....
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That's much clearer...thanks for your times guys...you rock..
But one more question...is there a way to use Raid 0 and Raid 1 at the same time? would I require three drives for this? 2 striped and one mirrored?? Just curious about it..seems really interesting..The only beans I like are Jelly Beans!!!
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SATA Raid 0 is expensive. 0+1 even more so.
I personally went for 2 x 120GB SATA drives in Raid 0 with some fans cooling the drives and double backup all critical data regularly onto CD & DVD. If the worst happens, I still have all application installation CDs so only a new disk is needed and no disaster.......hopefully.
"Don't eat yellow snow"
Martin
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raid1 is about the same as no raid, sometimes faster, sometimes slower.
http://www.tomshardware.com/storage/20020830/ide_raid2-07.html
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Well...the mobo that I want to get is the Asus K8V Deluxe and it suports Raid 0+1...so I'm guessing that I will be able to use both...So if I wanted to use both I would need 3 HD right?? HD1+HD2=Raid 0 and HD3=Raid 1...is this "theory" correct? I know that this mobo only supports only 2 SATA HD..but it also supports UDMA 133...is there a problem with that at all??? Thanks everybody for your help...sorry if I sound like a dumba**!
The only beans I like are Jelly Beans!!!
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Check out this site. Explains different RAID confiurations. I thought there were 5 but looks like 10 or more.
http://www.acnc.com/04_01_00.html
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Thanks for the link OntheHill...very, very helpful...I guess that my "theory" was wrong...if I wanted to use Raid 0+1 I would need at least 4 drives and not 3 like I thought...
I still wonder why though...shouldn't they come out with some kind of Raid that I'll be able to strip and mirror with just 3 drives???????
Thanks for the info anyways...I'm gonna save that link for future use..The only beans I like are Jelly Beans!!!
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Hi
I have a doubt, we have Compaq server, company is planned to buy six hot swappable Hard Disk,
Can I create, first mirrored with two hard disk and after completing this can I create RAID5 with remaining four Hard disk.That is, we wanted to have redundancy for operating system, therefore Mirroring with two Hard disk.
Later we want to create the RAID5 with remaining four Hard diskPlease any explain on this,
Regards
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I don't think it would support having a Raid 1 and Raid 5 from what I understood in the tutorial that OntheHill provided me...plus..if it did..it would be expensive as hell...I could be wrong though...let the experts answer you...
The only beans I like are Jelly Beans!!!
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It is loosely correct to say that striping means a file is split between drives.
Raid does not deal with files. It deals with blocks. I know that is a small point but its like the OSI model. You need to understand what is happening at each layer.
"If you mirror your tranfer speed is actually lower than with one drive due to the overhead of the controller. Add to that the ECC memory usually used with such systems and you take another performance hit. "
This statement is incorrect. First, Disk I/O is much slower then any transaction being done in memory no matter what the type. ECC memory does not slow your system down but provides additional error correction on the fly in case its needed. Memory is measured in nanoseconds and drives are measured in microseconds.
It is also incorrect that transfer speed is slower with mirrored drives. Data being written to the drives is a bit slower due to having to do dual writes. Your controller is the biggest factor here and if it can perform the writes simultaniouslyby lining up the read/write heads. The great thing about mirroring is you can read from both drives at the same time! This increases read performance which for most of us [and the OS] is what occures more often then writes.
Raid 0+1 is a stripe of mirror sets. This gives you performance of stripe but the fault tolerance of mirror. Problem with this config is if you lose one drive you have lost your fault tolerance. This is a setup that mandates a/multiple hot spares.
Raid 10 is stripe sets that are mirrored. Better fault tolerance then raid 0+1 but more drives/cost. Excellent performance though due to the stiping.
If you have 6 drives it is recommended that you mirror the OS and raid the data. Every controller I have worked with over the last 12 years supports this configuration. I personally try to stay away from raid5 but do 0+1 and 10. There is a major difference in performance when compared to raid5.
There is the issue of pagefile operations [ms says no raid1 or 5 - they are wrong concerning raid1 as they are in a number of aspect of pagefile operations but that is another discussion].
If you are going to raid5 your data only use THREE DRIVES. Save one as a HOT SPARE. A hot spare will automatically take over for a failed drive in either raid set. I can't tell you how many times that has saved my bacon. Much easier to down the server at non peak hours to install/reconfigure a replaced failed drive as a hot spare then have the chance that a second drive die in the raid5 which means you are only as good as your last backup assuming a 3 drive config.
Another trick for raid optimization that is commonly overlooked is to use dual or triple channel raid cards. For example if you put one drive on one channel and another drive on another channel then raid1 you get better performance then if both drives were on the same channel.
Another aspect to be aware of is how many drives you put on a channel. Raid cards support up to 15 devices but I have seen bus slowdown due to this configuration. My observation is you are compromizing performance when you get past 5-7 drives per channel. You NEVER want to mix slow drives with fast ones on the same bus or put devices like tape drives/cds/etc on the same channel as your raid array. You will take a major performance hit as the bus slows down to address the slowest device.
Another issue [gee I say that alot] is drives. Usually when you buy drives they are out of the same lot. This also means then can FAIL ABOUT THE SAME TIME. If at all possible get the same drive/manufacturer but different lots. I have had this experience of a mirror set failed. Before the hot spare rebuild could finish the 2nd drive in the mirror set died. That was not a fun day.
I hope this has been helpful.
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Have have recently heard of Raid 1+0 (not 0+1) which is Raid 1 (mirrored) BUT its read as a stripped drive (Raid 0). Thus you get the benefits of not loosing data should the drive fail, only using 2 drives and the added speed of reading stripes.
BUT I cant find where I heard of it, and I have looked for an adapter but cant find one. Its difficult to use 1+0 in search engines such as google, and some companies list 0+1 as 1+0.
Can anyone help me???
I have a a lovely Asus P4P800 3.2GHz 400FSB, 1GB TwinX Corsair memory. But my Deskstar 120GB drive is quite slow in comparison to the rest of the system. It has a built in Raid controller but I am not forking out for 4 Sata150 drives, or another 3 Deskstars.
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