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RAID question

Posted on 2004-04-08
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Last Modified: 2010-04-19
I'm setting up a proliant server as the configuration follows:

Primary scsi drive 1st controller 36gb - windows 2003
Primary scsi drive 2nd controller 76GB - DATA Mirrored - RAID1
Secondary scsi drive 2nd controller 76GB - DATA Mirrored - RAID1

Now is that a bad setup? Is there a way to turn the raid 1 drives to become dynamic, I did not see that option on the disk manager.

Thanks
jdff
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by:jdff
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If I would do raid5 I would not have redundancy, is that right?

jdff
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by:What90
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Hi jdff,

What you have is fine, however if can get more money if try this:

If possible I'd get a second 36 GB disk and mirror the windows 2003 partition for redundancy.
Then, if your using the data partition for mission critical storage get a third  76GB and set the drives up as RAID 5.

My reason why would I make the DATA be RAID 5 rather than RAID 1 is that with RAID 5 I can expand the RAID volume by simply adding disks. with Mirrored RAID it isn't so easy.

Is there any particular reason you want to use dynamic rather than basic on your disks?  
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by:jdff
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well if I don't make the 76GB RAID1 I will have no redundancy right? the 76gb is the DATA hard disk so I think I have to give priority to the data, don't you think? setting up as RAID5 will give me the ability of expanding later on but no safety on the data when comes to hard disk failure, Am'I correct?

Isn't dynamic partitions faster than basic?

Ok, now let's try a different question, what would be a good setup in order to read/write files of the server through the network?

Thanks, I would appreciate advices and experiences.
jdff
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by:Fatal_Exception
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RAID 5 by definition provides the best redundancy you can have..  It just adds a parity stripe so when a drive fails, it can be swapped out and regenerated on the fly..  Definitely consider the higher RAID configuration..  The ONLY drawback to 5 is that you loose one disk to the parity stripe (worth of space), so if you have 3 drives in a RAID 5, then you only have 2 drives worth of space.. If you have 4 drives in the RAID, then you have 3 disks worth of space..  

FE
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by:Fatal_Exception
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Additionally, RAID 5 offers much better performance than a mirrored drive...  forgot to put that in...  Because it is striping the drives with data, the speeds are much, much better..

here is an overview of RAID 5..  note the last paragraph..

http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel5-c.html

FE
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by:jdff
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so let's say that the 2nd drive of the raid fails, Am'I able to install a new drive and recovery the data that was on the bad drive? Or I lost the entire raid thing and my data?

Thanks
jdff
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by:jdff
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Also,
Isn't dynamic partitions faster than basic?

Thanks
jdff
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by:What90
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jdff,

For the best read/write speeds RAID 1 is bettter that RAID 5

If three disks is all you have then your current suggestion is the best option (System disk RAID 0 and 2 data disks RAID 1)
If you had four disks  - 2 System disk RAID 1 and 2 data disks RAID 1
If you had five disks - 2 System disk RAID 1 and 2 data disks RAID 1 + 1 disk as hot swap or 2 System disk RAID 1 and 3 data disks RAID 5

This should help firm up what the different types of RAID are for:
http://www.melbpc.org.au/pcupdate/2306/2306article6.htm


Ms Dynamic disks have the following advantages:

http://www.microsoft.com/windows2000/en/server/help/default.asp?url=/windows2000/en/server/help/sag_DISKconcepts_04A.htm


My personal view is that RAID 5 is the way to go with data as it's fault tolerent and expandable. Most of the data i put on RAID 5 disks doesn't need masive read/write speeds (usually MS office files).
 I use RAID 1 for system disks and log files (Exchange/SQL) for the speed factor.

Hope that helps!
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If the first, second or any single drive in a RAID 5 array fails, then you just replace the drive and it is automatically regenerated..  that is what the parity stripe is for, to keep the data intact and to easily replace the lost stripes..  The mirror raid drive is just a mirror of the original..  these tend to be nice if you cannot afford the higher order RAIDs, but not nearly as efficient...  

If you are using a Hardware RAID (special raid controller cards) then you do not have to worry about basic vs dynamic..  These come into play when using software RAID..  In fact, in a software RAID, the disks must be dynamic disks..  Basic disks do not support RAID configurations in Windows...
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by:Fatal_Exception
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Here is a little on software RAID 5 when done within Windows..   Again, these must be dynamic...

http://www.winnetmag.com/Article/ArticleID/14675/Windows_14675.html
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by:jdff
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But what you do when one hard disk crashes out of raid 1 or 5? I would like to go ahead and use raid5 but the thing is that I think if one drive physically crashes it does not have the ability of bringing the files back on new replacement drive, Is this correct?


Thank you for your time.
jdff
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by:Fatal_Exception
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BTW:  What90..  hope you do not mind me buttin in on this thread..  just bored tonight I guess...  :)
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by:Fatal_Exception
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NO....  That is what RAID 5 is all about...   They definitely have that capability..!!!!!
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by:Fatal_Exception
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Read that link I posted above, or the one W90 mentioned...  It is all about the parity stripe...!!  very cool, and highly recommended..!!
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by:jdff
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Ok, so now I understand a bit, so the RAID5 will regenerate the files into the new drive because the parity stripe. Is there any circumstances that raid5 will completely fail? Does every drive on RAID5 has the parity stripe of the other drives?

Thanks
jdff
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by:What90
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Fatal_Exception,
Missed you posts - damned QuickPost not refreshing ;-)

Have a great Easter!
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by:Fatal_Exception
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Correct..  the parity stripe is created on all drives, meaning that when any one of the drives fails, it can be regenerated from the other drives...   Of course, if multiple drives fail, then you could be in trouble, but the chances of that are slim, and that is why we have backups, right..??
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by:Fatal_Exception
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*grin*  I gave up on QP...  not that it did not do the job, but just did not want it running in front of me all the time...    I too missed some posts with it, so I just count on my email refreshing every minute... lol, eh..?

And happy Easter to all of you..!!

FE
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by:What90
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jdff,


Say you have 3 RAID 5 disks, then two of them fail - you can still regenerate the data for the last disk. You'd have to destroy the entire RAID 5 array (all 3 disks would have to fail) That why most of use love RAID 5!
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by:Fatal_Exception
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:)  Next best thing to NEVER HAVING TO WORRY..!!!   Disaster Recovery can take years off an admins life..!!!  Knock on wood..
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by:Gareth Gudger
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Actually I thought only one disk was allowed to fail in RAID 5?
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by:What90
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diggisaur - your correct, but obviously depending on the RAID 5 disk numbers.

I've seen a 3 disk RAID 5 array lost two drives, which stopped it being operational but the data was recovered from last good disk and the RAID array was rebuilt. Jusy one of the reason I convince the money men to spend that little bit more on data protection from RAID 5.
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by:Fatal_Exception
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And what are the chances that 2 drives are going to fail at once..??   It would have to be something major, like a tremendous power spike, which is unlikely if you are using good protection and a UPS....   The parity stripe keeps info on everything that goes on the disk array, so the entire array can be rebuilt..  and obviously, the more disks, the better..

I even like to put 'hot spares' in my servers, which just sit there until needed..  And the good servers come with SCSI arrays that are hot swappable..  meaning you can replace the drives on the fly..  

Good morning everyone..!!  
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by:What90
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jdff,

Did you make a choice on what was best for you?
What did you choose?
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by:Fatal_Exception
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Thanks..  glad we could help..

FE
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by:jdff
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What90 thank you very much also for your time and explanation, I accepted FE's comment cause that one was very clear on what I was trying to understand. You did a great job also and I'm sure you'll be able to help me another time.

Thanks
jdff
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by:What90
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No problem, my spelling and typing skills stink, so I prefer to cut and paste links rather than confuse the buggery out of folks trying to follow my personal instructions ;-)
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