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HP15500 - Migrate from a RAID 1+0 to RAID 5

Posted on 2008-06-23
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Last Modified: 2013-11-14
Good Day,

I have a MSA 1500 CS with on box attached & 12 300GB Drives.  I have two unassigned drives @ this time & I want to convert one of my RAID 1+0  (2 drives) to a RAID 5.  If I click on the Migrate RAID & move it to a RAID 5 Fault Tolereance, will I lose the data on those drives or can this be done without losing all data?
(granted - I will have full backups before I do this)

Thanks!
James
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Question by:deathandgravity
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by:eatmeimadanish
ID: 21858850
you can not change raid configs and keep data.  I would make a backup, change the raid then restore that backup.  The reason you can not change RAID configs is because the striping is contained on the drive itself, when that gets purged with the new RAID all that information is overwritten.
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by:deathandgravity
ID: 21858988
thanks - that't what I needed.
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garycase earned 167 total points
ID: 21859757
It's good to assume that's true (i.e. be sure you have a complete backup) ... HOWEVER, it depends on the specific RAID controller and what it supports.   If the RAID management software has a "Migrate" option, it most likely does so without data loss => that's what "migrate" means :-)     Otherwise, you'd simply delete the current array and create a new one.

Back your data up, then do the migration --> chances are very good the data will be just fine :-)
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by:eatmeimadanish
ID: 21860600
I am not a big fan of the migrating solution for two reasons.  1) It tends to take an absurd amount of time depending on data size, and if it fails at any point during the process you end up restoring anyway and just wasted all that time.  2) I have had problems in the past with data integrity after this process is done, whether it be due to massive file fragmentation or just bad partitioning, in which case if this does happen you end up not finding out until production hours and then have to take the system offline again and just restore from backup anyway.

Its a good idea to follow the moto, do it right the first time.
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by:garycase
ID: 21860783
As I noted, it's always a good idea to have a full backup (which the author has indicated he does ... or will).   But as for doing it "right" => the RAID management software supports migration ... so there's nothing "wrong" about using that capability.   The question was whether or not the RAID can be changed without losing the data ["... will I lose the data on those drives or can this be done without losing all data?"] ==>  The answer is No, you won't lose any data ... that's what "migration" means.   Your answer ["... you can not change raid configs and keep data ..."] was WRONG.   You may not agree with using the data migration facility ... but in that case a better answer would have been to note the reasons you don't like doing it that way (which you did in your last post) rather than stating an incorrect answer.
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by:eatmeimadanish
ID: 21861012
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=130&prodSeriesId=415598&prodTypeId=12169&objectID=c00677849

Fixed deadlock issue that occurs while performing IO during RAID migration.

You need to calm down.  I was merely citing enterprise level experience with known issues with the migration process.  Unless you are completely familiar with the step by step process and can outline that for this typical setup, then usually the best answer is the safest answer.  This becomes the right answer in any enterprise environment.  Yes, this "may" work and in most likely will if all the moons are aligned (right firmware, correct setup of equipment, stable equipment).  And just so you know, all of the documentation states you can move from RAID 5 to RAID 6 in the migration path, I see nothing in the documentation that says otherwise.  So unless you can verify your claim and provide documentation that moving from a RAID 10 to a RAID 5 can happen with the MSA 1500 CS than i would be careful with arguing your point.  

My computer can read minds, under the right circumstances.  This doesn't make the statement "computers can't read minds" wrong.  
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by:andyalder
ID: 21864117
It's a bit much making a bald statement like "you can not change raid configs and keep data." when it's totally incorrect. The MSA1500cs controllers are based on the same algorithms (and some of the same chips) that the Smart Array 6400 controllers are based on, migrating from RAID 10 to RAID 5 is supported.
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Assisted Solution

by:eatmeimadanish
eatmeimadanish earned 166 total points
ID: 21866904
Well I did not come here to argue... It is a true statement that if you change the RAID config you lose data.  The migration utility is subjective and up for debate, but regardless you have yet to point to a single document or provide instructions on how to actually accomplish this task.  

I come here to Experts Exchange to offer sound advice and to make sure people are successful the first time.  Not to argue points based on nothing but conjecture.  You have no idea if that device can actually successfully migrate a RAID 10 to a RAID 5, and merely changing the RAID type WILL destroy the data.  And until you can substantiate your claims, the advice that needs to be given is the one that is guaranteed to work.
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by:andyalder
ID: 21867160
Of course I know that it can do it; I'm a Proliant ASE and a StorageWorks Master ASE. RAID level migration is performed in the workshops you have to attend to get those qualifications and I've also done it in the field.
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by:andyalder
andyalder earned 167 total points
ID: 21867492
Here you are look, there's a bug with the SA431, it refuses to migrate RAID 1 to RAID 5 with one version of firmware - http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c01203208

(as I said before, the MSA1000/1500 controller is based on the smart array family of PCI controllers, right down to the PCI-X bus inside it.)

I'd rather add both extra drives and let it migrate them from 2 disk to 4 disk RAID 10 though, RAID 10's so much faster.
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by:garycase
ID: 21867646
"... Not to argue points based on nothing but conjecture ..." ==> Just FYI, neither Andy nor I post comments based on conjecture :-)    ... and as I noted earlier, and Andy eloquently repeated, it's hardly in keeping with the "Expert" in Experts Exchange when you make statements that are completely incorrect [i.e. "you can not change raid configs and keep data."].
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by:andyalder
ID: 21868001
I sometimes use a bit of conjecture but I make it quite obvious when I do. e.g. "I do not think it will allow online RAID level migration if the cache battery is flat/faulty", and "it will probably take about 100 hours for the migration to complete but the data is usable while it's happening". 'probably' and 'think' indicate I'm not quite sure.
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by:garycase
ID: 21868192
... Yes, I suppose I should have caveated that statement.   I do the same thing ... but I make it VERY clear when I do, with similar caveats ("not sure",  "haven't tried this, but ...", "might work", etc.).   Otherwise my comments are based on experience, not conjecture :-)
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by:deathandgravity
ID: 31469878
Ok& Very lively discussion.   Thanks for the input/information.
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by:andyalder
ID: 21901973
How can you have an assisted solution that is completely wrong selected? Just about every SAN box I've ever played with has the option to migrate RAID levels, change stripe size etc on the fly with no loss of data and only a very low performance hit during the data-shuffling. They take so long because they preserve parity during the migration and keep track of how far they are through the task in the metadata.
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by:garycase
ID: 21902110
I had the same thought :-)
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