topic Re: RAID 5 in Operating System - Microsoft

RAID 5

Abdul R. Arab — Mon, 16 Apr 2007 09:37:16 GMT

I have an HP ProLiant ML370 Series server with 3 72GB hard disks devided into 2 partitions C & D.
If i enter to the device manager i can see only two hard disks installed while physically i have 3.
I need an explanation to that please.

Also the RAM capacity is 4 GB. If i enter to the BIOS i can see the correct capacity of the RAM while if i right click the "My Computer" and go to properties i can see the RAM capacity is 3.25 GB
Kindly explain.

Regards,
Abdul R. Arab

Re: RAID 5

Ivan Ferreira — Mon, 16 Apr 2007 09:47:57 GMT

1- As your subject says, RAID 5 makes the 3 disks as one disk, using one of the disks as parity, so if one disk fails, data is not lost.

You see two disks in windows because you have two partitions in the RAID 5 disk.

2- You must alter the boot.ini file to include the /PAE boot option to be able to detect all memory.

If you don't plan to install linux later, you missed the forum ;)

Re: RAID 5

Court Campbell — Mon, 16 Apr 2007 10:43:53 GMT

woo, I would never say raid 5 uses one disk for parity. the parity is distributed across the disks. If only the one disk had all the parity data you would be up a creek if you lost just that disk.

Re: RAID 5

Uwe Zessin — Mon, 16 Apr 2007 11:48:01 GMT

> If only the one disk had all the parity data you would be up a creek if you lost just that disk.

Hm. I disagee, because you still have all data on the remaining data disk drives. You are now running a RAID-0 set. Of course, it cannot withstand the loss of one more disk drive, but RAID-5 can't do that either.

What Ivan has described (multiple data disk drives with all parity stored on one disk drive) is called RAID-4. The problem with this is that it is not good for a large number of writes, because the parity disk drive is always being hit.

RAID-5 works around this by distributing the parity data across all disk drives in the RAID set.

Re: RAID 5

Ivan Ferreira — Mon, 16 Apr 2007 13:00:14 GMT

>>> 1- As your subject says, RAID 5 makes the 3 disks as one disk, using one of the disks as parity, so if one disk fails, data is not lost.

This was a simple explanation. If you want a more "strict" definition, consider "the space of one disk" for parity. Most people know that the RAID 5 parity is distributed.

And for strict definition, it's not a RAID 4, maybe a RAID 3.

Re: RAID 5

Court Campbell — Mon, 16 Apr 2007 14:23:31 GMT

Uwe, I agree. I wasn't thinking.

Ivan, not trying to be picky, just wanted Abdul to have a more accurate description of raid5.

Re: RAID 5

Uwe Zessin — Mon, 16 Apr 2007 23:47:12 GMT

> it's not a RAID 4, maybe a RAID 3.

Both, RAID-3 and RAID-4 use a dedicated parity disk drive, but RAID-3 uses a MUCH smaller chunk size than RAID-4 and RAID-5.

Re: RAID 5

Abdul R. Arab — Tue, 17 Apr 2007 01:25:41 GMT

Thanks guys for your reply, but i still need a small help from you regarding the RAM issue.
Ivan and all, would you explain more on how to do it.

Regards,

Re: RAID 5

Ivan Ferreira — Tue, 17 Apr 2007 08:27:46 GMT

Here is a thread where explains how to do it:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=1009988

Cheers.

Re: RAID 5

Abdul R. Arab — Tue, 17 Apr 2007 08:52:59 GMT

Ivan i would rate your reply 100 instead of 10:)
Thanks alot you bailed me out of a dilemma :)