PE 4600: Splitting backplane - daughter card, please help!

Karthik Viswanathan vkaru at iastate.edu
Fri Oct 17 17:35:01 CDT 2003


At 05:04 PM 10/17/2003, you wrote:

>You are correct that a RAID0 is a stripe across all disks in that array, so
>the data is spread out across them.  And, there is no redundancy in this
>type of RAID so if you lose a drive you will lose the entire array and will
>have to restore all files from backup once you have the drive replaced.
>But, depending on what is on the stand alone drive you lose, you could be in
>the same boat.  Where is your OS going to be located?  On one of the 146GB
>drives?  What if that is the one that fails?  Your system is down until you
>get the drive replaced and the files restored.

Yes you are correct.

>  What if it's just your user
>directories?  Well, those users can't login and do anything until the drive
>is replaced and the files restored.  So, if drive failure is the main
>concern, then you really need to consider a RAID configuration that has
>redundancy, which would be RAID1 with two disks.

The main problem is I cannot loose half the disk space and also cannot 
afford for an additional 146G hard disk :-(. Considering this situation I 
thought of not putting the raid on it. Could you suggest me where I should 
install the operating system (linux), on one of the 146G hard disk or on 
the 18G array on RAID)?


>As for the 18GB drives, RAID0 will obviously be faster than RAID5 because
>there is no computation in RAID0 of a checksum as there is in RAID5, but
>like I said RAID0 has no redundancy where RAID5 does.  There are several
>documents available on the web in regards to the advantages and
>disadvantages of the different levels of RAID.  There are also several good
>documents on the differences in speed between the different levels of RAID.
>I would suggest going to google (or your favorite search engine) and looking
>for some of these documents to decide what is best for your environment.




>The PERC3/DC is a SCSI controller, like the on-board SCSI controller.  The
>difference being the PERC3 has it's own processor and memory and software so
>that it can take the SCSI drives connected to it and build RAID arrays with
>them, if you want.  So, with both the on-board SCSI controller that has two
>channels and the PERC3/DC that has two channels, you actually have four SCSI
>channels available in your system and two of those four can be used to
>control RAID arrays.  There is no connection between the on-board SCSI
>controller and the PERC3/DC.  They are two completely separate SCSI
>controllers.  They will be used to control completely different SCSI
>devices.
>
>Data that needs to go to a device (RAID array or stand-alone device) on the
>PERC3 will go directly to the PERC3 and the on-board SCSI controller will
>never know about it.  Data that needs to go to a device on the on-board SCSI
>controller will go directly to that on-board SCSI controller and the PERC3
>will never know about this.
>
>Hope that clears it up some.

Excellent!! I think I have better understanding now. Thanks a lot.

Karthik






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