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install new drives in RAID 5 array

Posted on 2009-05-01
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I want to install new hard drives into an exisiting Dell server.  Current configuration is three hot swap, 146 GB drives in a RAID 5 array.  There is one open bay for a fourth drive.  I want to install four 1TB drives in a RAID 5 array.  I know I will have to remove the three 146 GB drives and then use the Dell Open manage utility to install 2003 Server OS and create the new array.
 I will copy all the data to another server and also have a backup of it before proceeding.  I plan to copy the data back to the new drives when done.
My question is if something goes wrong when setting up the new drives, if I shut down the server and plug the old drives back in, will Server 2003 boot and will all the data still be there?  Any input about this procedure is appreciated.  Thank you
CJA
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Question by:cja-tech-guy
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by:chuckyh
ID: 24279912
If something goes wrong, you should be able to plug your 146gb drives back in and be back to where you started from. The RAID card may bark at you for a configuration change but it should boot backup etc. The RAID configuration is stored on the drives as well as the RAID card.
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lnkevin earned 2000 total points
ID: 24280287
You should be able to plug the old drives back and resume the business. However, there is one critical point that you will not want to miss: MARK YOUR DRIVES IN ORDER. Make sure you take a marker and mark the order of the drives so just in case you need to put them back, you don't mix up the order.

Other thing is you want to make sure your Dell server supports 1TB drive and over 2TB of space. Check with Dell support or google your server model specification for details.

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by:andyalder
ID: 24286726
It'll be quite a bit slower than before, but I guess you want space rather than speed.
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by:cja-tech-guy
ID: 24295169
andyalder
Please explain why it will be slower.  
Thanks,
cja
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by:lnkevin
ID: 24295255
We all assume your 1TB drive is SATA vs 146GB SAS. If your 146GB is SAS, you downgrade from SAS to SATA and the performance is downgraded as well.

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by:cja-tech-guy
ID: 24295505
How noticeable will the slowdown in performance be?
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by:lnkevin
ID: 24295792
Serial ATA 2.5 provides a maximum bandwidth of 3 Gbit/s per port, if you have 3G SATA drive and controller. SAS provides a maximum bandwidth 6 and 12 Gbit/s, resulting in 600 MB/s and 1,200 MB/s bandwidth per port.

http://www.tomshardware.com/reviews/UNIFIED-SERIAL-RAID-CONTROLLERS-PCI-EXPRESS,1665-2.html

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by:andyalder
ID: 24295802
It's not so much the interface that matters but the physical disk parameters, you can aproximate a read/write operation to take half a disk turn plus an average seek.

Half a turn is 30,000/RPM = 2ms for a 15K, 3ms for a 10k, 4.1ms for 7.2k
You'll have to look up the average seek of your disks, neither Dell nor HP make the disks so http://h18000.www1.hp.com/products/quickspecs/12244_div/12244_div.html is a fairly good list - average 3.5ms for 15k 146GB LFF (10ks are about 4ms), 7.4ms for 1TB.

So 5.5ms for 15k 146GB, 11.5ms for 1TB. but those seek speeds for the 1TB look high to me, 11ms is more like it giving over 15 ms for 1TB SATAs. In other words your new disks are 1/3 the speed of your old ones for random access, they're really fast for backup, archiving and video streaming though where they are driven sequentially.

You'll have to look up the parameters yourself on Dell's website, but I doubt these are far off. You should also check what duty-cycle they claim for them, 7.2K disks aren't normally designed for 24x7 operation. You do of course have one more disk in the new array so it's not going to be 1/3 of the speed it was before, nmore like half as fast.
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by:andyalder
ID: 24296078
I don't bother to take into account the bus bandwidth, say for example you were doing 64k random blocks, SATA transfer time would be 0.4 ms, SAS 0.2ms so it's swamped by the physical disk properties.

Hey look, pretty pictures :) http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01460725/c01460725.pdf (again HP rather than Dell but doesn't make much odds.
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