Question : Problem: Raid 5 vs Raid 1

G'day,

I'm setting up a server thats running a file storing applciation - essentially a file server.

I'm trying to decide between Raid 1 and Raid 5.  Obviously the efficiency of Raid 5 appeals to me.

My questions:

1. i understand that RAID 5 uses several data disks and one parity disk - how are these configured?  i.e. if my server takes 9 hard disks - how many of these would need to be parity disks and how many could be data disks?

2. upon drive failure - with RAID 1 - rebuilding is easy right - I just copy the contents of teh non-failed drive in a pair onto a new drive and put it in.  How does rebuilding work with RAID 5?  do you have to take the whole server offline to rebuild?  Can you rebuild with the server still up like with RAID 1?

Answer : Problem: Raid 5 vs Raid 1

RAID 5 doesn't use a dedicated parity disk.  It uses parity over all disks.  ANY one disk can fail and you'll keep running.  Total available space will be GB(disks - 1).  So if you have 9 100GB drives, you'd have 800 GB of available space in a configured RAID 5

Rebuilding depends on how you implement RAID - Software or Hardware?  

If software, RAID 5 is managed through Computer Management/Disk Management.  The system will slow down somewhat (as it will have to reconstruct the lost data) and event log messages will appear concerning the failed disks.  You can probably configure Windows alerts to notify you as well.  Once you know you have a failed disk, you can replace the failed disk (make sure you don't replace a working disk by mistake) and tell windows to repair/rebuild the RAID.

If software, a RAID 1 mirror should just keep working with little or no degradation in performance, but obviously no redundancy.  The exception to this is if you use RAID 1 on the system disk.  If that fails, the system will go down.  You would then have to reboot to that disk, using a different entry in the boot.ini file (change the ARC path).  Windows 2003 server does this for you, 2000 you must do it yourself.  Replacing a failed disk is simple.  Just break the existing mirror and remirror to the new working disk.

If hardware RAID 5, there will likely be 3rd party software to manage the RAID array, which likely would include some notification routines.  Assuming Hot-plug SCSI or IDE devices, you can then replace the bad drive and the controller should detect the new drive and, depending on the controller, it might automatically start rebuilding the RAID for you.  Otherwise you'd have to initiate it.

In my opinion, hardware RAID is the way to go, RAID 5 with a hot spare.  Problem is finding a reliable SCSI RAID controller and external SCSI devices.  I've used Dells in the past and HATED them.  50% failure rate (or so) in my experience (using combinations of PERC2/PERC 3 controllers and 200S/210S/220S arrays).  Never used the hot-plug features of a 3ware ATA or SATA RAID card - they might be your best option.

Software RAID is fine, but it requires conforming to a Microsoft way of things - something I just don't like.