Array configuration at HP Proliant ML 370 G5

Hi There experts,

I have purchased a new HP proliant ML 370 G5 server with four  300 GB SAS hard drives, It has HP smart array  p400 array controller, i would like to dedicate it for file server, what is the best configuration of the array to make fault tolernce and also hot swapable,

thanks

concern_supportAsked:
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Rick FeeMessaging Engineer - Disaster Recovery EngineerCommented:
I would setup it up with RAID 5.

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concern_supportAuthor Commented:

thanks you very much for your quick response, But i was thinking that i would like to  configure first two sas drives fro the operating system redudancy and the other two for file server data storages, also i would like to swap one drive on each friday for offline backup, is there these facilities availiable,

i am completely new with Array technology if there are any mistakes apologies me,

thanks
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Alan HardistyCo-OwnerCommented:
What you are describing is using RAID 1 (mirroring) for both system volume and data volume.
This will reduce your disk space down by 50% from the 4 drives you currently have as you need two drives per volume giving you 600Gb total space.
If you chose to configure the drives as RAID 5 with a hot spare, then would still have 600Gb of space, but your system would self-recover if a drive failed as the Hot-Spare drive would kick in immediately and the data on the failed drive would be wriiten to the new Hot-Spare drive.  You could suffer the loss of 2 drives with this configuration without any problems.
If you suffer 2 drive failures in a Mirrored (RAID 1) configuration, you would lose the entire volume if the drives lost were on the same array.
I would never recommend using the server drives as a backup by pulling a drive out (even on a weekly basis) as this will give the server extra work to do by re-mirroring the drives every week.
You would be better off investing in a tape backup system, or disk imaging backup system to perform proper backups, the tape backups giving you the ability to recover hostorical data and the disk imaging backup to allow Disaster Recovery of the system and immediate restore of files deleted over the past few days (or for as many days as you can store images for).
RAID 5 is expandable - you can simply add more drives, configure the array to use the additional space and then allocate the additional space.  RAID 1 is not expandable.
It's ultimately your call - but I would never recommend the solution you are thinking of.
lan
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KrisdeepCommented:
Nothing surpass raid 1+ 0 also know as raid 10. Below is a better explanation.

http://decipherinfosys.wordpress.com/2007/01/30/what-raid-is-best-for-you/
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Rick FeeMessaging Engineer - Disaster Recovery EngineerCommented:
I agree with alanhardisty.    For file servers (and most others) I like to get two 72GB drives and mirror them for the OS.    Then RAID 5 for the data store.    I would setup a solid backup solution, lost data is extremely costly.
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gikkelCommented:
I'd recommend you buy two more smaller drivers to run the operating system and keep it separate.  You really shouldn't need much more than 147gb, and can probably even get away with 73gb without any issues for quite some time and run that in a raid 1.  If you plan on using virtual machines, use the 147gb drives.  There are so many different factors that decide which raid configuration to use and there will most likely be 30 more comments giving you different ideas and why it should be done that way.  

Bottom line, RAID 5 is the best bang for your buck.  Its not as fast for write operations as RAID 10, but read times are similar.  The P400 is a decent controller...it'll handle RAID 5 just fine. Unless you're using this for a database server, you'd probably never recognize the difference.

I think everyone will agree this isnt a bad way to start out your setup:
RAID 1 for your OS - 2 73GB or 147GB sas drives (you could even use enterprise sata drives)
RAID 5 for your file storage, use 3 of the 4 drives and keep the additional drive as a hot spare.  If you really think you'll benefit, you can configure in RAID 10...just remember its very costly to upgrade.
Backup to tapes or SATA drives
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concern_supportAuthor Commented:
thanks very much for all of your comments, i would like to purchase two other 147 GB drives and would mirror them with raid 1.
as i am new with the array how can i use a hot spare hard drive in my raid 5 configuration, now i have added all these four disk to raid 5 with four logical drives configured, will you please kindly guide me how to configure a hard spare drive, i would like to use three disk in raid5 and use one of them as hard spare,

if i do use these four disks in raid 5 with one logical drive , will i face any problems with raid 5.

your commnets are appreicated,

thanks
 
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Alan HardistyCo-OwnerCommented:
You will need to use the HP Array Configuration Utility to configure the arrays.
Select the two 147Gb drives and create a RAID 1 array (Mirrored) for the OS, then select the 4 300Gb drives and create a RAID 5 array with Hot Spare.
You won't face any problems with a RAID 5 array (with Hot Spare) - the disks will get you out of trouble if a drive fails as the Hot Spare wil immediately kick in and the data will rebuild itself using the information on the drives and the Parity (checksum) info.  Basically data is written on two drives and parity on the third.  As we are talking 0's and 1's at the disk level, it is simple maths.  Drive 1 has a 1 written to it's disk, drive 2 has a 1 written to it's disk and the 3rd drive has parity which would be a 0.  If any drive fails, the remaining data can be used to detemine what was on the failed drive and simple maths tells the disks what to write to the new disk.  (I may have my 1's and 0's around the wrong way but the principal is there) :-)
Once the hot spare kicks in, it will take a while for the data to be rebuilt, but there is no user intervention required.
All you need to do is order a new 300Gb HDD and pull out the failed drive and replace it with the new drive once the Array is healthy again.
Here is a guide to advise you about the Array Configuration Utility - http://docs.hp.com/en/9320/acu.pdf
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concern_supportAuthor Commented:
i selected the four hard disk and configured the array 5 but i could not see any option there with the hot spare,
is the fourth drive is treated hot spare autmatically, if it is yes then it means that i can take out the fourth hard disk and keep it in safe place which can be used when any dirve fails,

thanks


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Alan HardistyCo-OwnerCommented:
If you configure 4 disks as RAID 5, then you are using all 4 for the Array.  Pick three drives and configure the array as RAID 5 (needs 3 as a minimum) and you should see a Hot Spare option.
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Alan HardistyCo-OwnerCommented:
Here is a link to the manual for your controller:
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00572169/c00572169.pdf
You need to Assign A Spare Drive - bottom of P16.
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concern_supportAuthor Commented:
still confused with hot spare option , i have found and configured one hard drive as hot spare and what should i do with this, can i take it out and keep in safe place so when one  drive in array fails i can insert this ,
or it should be there in the array and i will use a fifth hard drive which can be inserted when  the problem arises,

thanks
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Alan HardistyCo-OwnerCommented:
You leave the Hot Spare drive sitting there in the server waiting for a drive to fail.  If you take it out - it is not a hot spare, it is a drive sitting in a box!
If a problem arises and relies on your swapping the drive, then you may miss the problem and a second drive could fail at  which time, your server will die.
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gikkelCommented:
The "HOT" aspect means its installed, powered on, and ready to rock.  Since it won't be a part of your RAID volume unless a drive fails, its considered a "SPARE" (like waiting on the sideline).  
If you take the extra drive out, it'll just be a "spare" and you'll need to manually swap it with the failed drive...by assigning the drive as a spare and keeping it installed, you can skip that step.  

To add some confusion (sorry), if a failure should arise, you can remove the failed drive and replace while the system is still running (if your drives are hot-pluggable), in which case the replacement drive will act as the new "HOT SPARE".  However, at that time you may need to initialize the drive for it to be recognized...but we can save that caveat for a later time.
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concern_supportAuthor Commented:
i have configured three drive in(bay1 ,bay2 bay3) as raid 5 array, and the hard disk plugged in bay 4 is a hard spare, for example hard disk in bay2 that is the part of array5 fails so the hard spare will take its space automatically,

if i have another spare hard disk laying with myself in my cupboard can i put that in bay2 where the failed hard disk was laying before, is this will be treated as hard spare automaticallly or i will configure all these things once again,

sorry for any mistakes in the question i am new to array so therefore i would like to know everything on it before moving to install operating sytem on this,

thanks




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Alan HardistyCo-OwnerCommented:
Bay 4 will kick in should a drive in bay 1, 2 or 3 fail.  You then pull out the failed drive and replace it with the drive from your cupboard.
RAID usually reverts back to it's original configuration, so if you don't replace the drive in bay 2, the drive in bay 4 will stay as part of the array, but in my experience, if you replace the drive in bay 2 , that will get absorbed back into the array (data rebuilt again) and the hot spare drive in bay 4 will become spare again.
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concern_supportAuthor Commented:
Thank very much alan , i am going to accept this as a sultion thank once again,
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Alan HardistyCo-OwnerCommented:
No problems - come back if you need more info or have more questions.
Alan
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concern_supportAuthor Commented:
HI Alan, what strip is best for raid array5.

thanks
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concern_supportAuthor Commented:
sorry Alan this is strip size for raid array5, which one is the best choice for array configuration

thanks
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Alan HardistyCo-OwnerCommented:
If you use a smaller stripe size you will save some space on the disks
If you use a larger stripe size your performance will increase, but you will eat up space a little quicker as some will get wasted.

I would go with 16k or 32k stripe size to get a good balance of power and economy
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