RAID controller on board and Card

we have come to know that some limitation on the RAID  controller pick from the onboard and card based

we have done the test on our few servers to check the RAID is working on the define Standard . we have realized that two servers didn't work after removing one  hard disk from the RAID 1 setup  server . When I check with the vendor and replay to me that server has the entry level RAID control card and without fixing the second hard disk will not going to work . So it means it will take some to rebuild the second hard disk . till that time server not in the online mode

if I want to go with the realizable RAID .we need to have the enterprise raid controller with hot shapeable HDDs  

please comment on the above with your expertise knowledge
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John TsioumprisSoftware & Systems EngineerCommented:
Simple truth ..on board RAID controllers won't provide Enterprise class "abilities"..
The first time i had to hot plug off a problematic HDD it was a shock to me that everything went smooth without BSOD and crashes...when the replacement came i just plugged it in ..the system rebuilded and everything was transclunted with just a performance penalty...
When it comes to servers or high class workstations you see clearly that what you pay is what you get...
curAuthor Commented:
I am totally agree with you . is it possible to work in the enterprise level without fail hard disk  without inserting into hard disk bay . I thought system will not work without the entire hard disk array . what is the best way to check the RAID is working on the well mentioned  server  .
some times our insurance parties asking us the show us the RAID setup in place . we have already showed them the hard disk RAID setup  . but their not satisfied with the given answer in terms of testing  RAID  ? I don't know the industry best practice on the testing of the live server RAID for insurance purpose
noxchoGlobal Support CoordinatorCommented:
The on-board RAID controller is a so called Fake RAID. Only the external PCI RAID controllers are considered to be real hardware RAIDs.
If you remove one drive from RAID1 on on-board RAID then yes, it will fail to boot. On Hardware RAID it will start with a single drive as well. Plus hardware RAID controller gives you HotSwap feature which lets replace the drive while the server is online.
curAuthor Commented:
In my case  entry level PCI card and didn't work after removing. I think my card entry level ?
what are the recommended hard disk type for critical application point to consider
Only SOME on-board raid controllers are  fake-raid chips which do no more than add HDD ports and let the BIOS do the work.  .. but that is the norm.

So before making a blanket statement that may have nothing to do with what you have in your possession, what make/model of motherboard do you have?  

But in general, if you are doing to be doing RAID1 then your O/S can do a better job of software RAID1 then the onboard controller.  The vast majority of the on-board controllers won't do things like read load balancing which your O/S-based RAID will do.

A premium RAID controller - costing hundreds of dollars or more will do read load balancing, and has onboard cache and NVRAM that will do things like online expansion of RAID1 -> RAID5 or add battery protection so no data is lost if you lose power.

Bottom line, you get what you pay for in RAID controllers, and most on-board RAID chips cost about $2.00.   But same is not true for host-based software RAID.  IT will outperform your fakeraid and many low-end PCI-based RAID.

P.S. the O/S-based software RAID1 WILL keep running if you lose a HDD, but certainly make sure both disks are in the boot path on the BIOS.   You can also start with one disk and do an online conversion to RAID1, and S.M.A.R.T. predictive failure will work, and you will be alerted for any HDD issues like bad blocks through your O/S event manager.  So no secrets about what is happening to both drives.

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