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How to setup RAID 1... Should i use Hardware or Server 2008

Posted on 2008-10-11
Medium Priority
Last Modified: 2010-08-05
I know in the past you should always use a hardware raid. Is the raid better in Server 2008 to do it software... Just looking to do RAID 1 for the OS... Whichever way you advise, please let me know the benefit of that way... thank you very much.

This is a server with:
Server board from asus
(2) 2gb FB-DIMM Ram = 4gb
OS drives are 7200 rpm sata 80gb western digital
Question by:JBergenske
LVL 42

Expert Comment

by:Paul Solovyovsky
ID: 22695993
If available always use hardware RAID.  It provides better performance and does not rely on the Operating system thus does not use the resources of the OS.  It is usually easier to recover when hardware raid is configured since it does not rely on OS.  Hardware RAID is faster, more reliable, and gives you better options in most cases such as raid migration and/or expension.

Author Comment

ID: 22696002
ok... so typically on a raid 1 through hardware.... if one of the disks gets corupt or dies what happens as far as the system... will it alert in os, would it shut down, etc? This is a Exchange Server with Active Directory... It is a bit of an important system to go down if and when it does...
LVL 23

Expert Comment

ID: 22696012
Software RAID is slow, and hinders server performance.

With the sole exception of ZFS on Sun platforms, or LVM mirror on Linux for secondary storage,  I have never seen a situation where hardware RAID performed acceptably.

I believe it's better in this situation to  use  hard drive cloning tools  to clone the primary drive to the second one,  and use  software to periodically resync the second drive than to use software RAID.

You will have downtime if your primary drive fails;  however,  software RAID is slow, and can expand downtime caused by other reasons.

Software RAID is less reliable than hardware RAID, in that you may wind up with data corruption,  if your operating system crashes.

Whereas hardware RAID provides better integrity of the drives  (provided the controller doesn't go bad),  and better handling of failure conditions;  including the fact many hardware controllers have good support for hot-swapping a failed
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LVL 23

Accepted Solution

Mysidia earned 2000 total points
ID: 22696018
Correction:  never seen a situation where software RAID performed acceptably.

Your write operations will be slow,  since every block write will have to wait until both disks have finished completing the write,  and your OS has to send the commands to both disks, and manage this entire process.

Rather than sending the command once, to the hardware controller; and the hardware controller commits the write very quickly to both disks.

Using software RAID more than doubles the number of I/O commands your OS must send to the disks.

Performance of software RAID while a volume is rebuilding is terrible, and your server may essentially be down the entire time it takes to sync up the replaced hard drive and bring it online.
With supporting hardware RAID, you can install the replacement drive without downtime.

Server performance will not be degraded so much  in fact, it will barely notice a drive has failed with hardware RAID1,   other than that you have vendor-provided monitoring software on your server to notify you,  performance should not  be degraded  during rebuild of the array.

For mission critical servers that need high availability, hardware RAID is a must,  not a luxury item.


Author Comment

ID: 22696126
Okay... I looked at the specs for my Motherboard... Here are the different choices for raid besides for using windows.

LSI Logic Embedded Sata Raid Setup Utility
Intel Matrix Storage Manager Option Rom utility
Global Array Manager

All three of these come with the server... The first two are prior to the loading of windows... Have to use a entry keey during boot like (ctrl + 1) to enter.
Global  Array one looks like it has software that is included on the server setup cd. Is this one still considered software raid, or is this just a gui for it.

Also, using one of the bios type hardware options, how do you know when a drive fails... Will it alert you in windows.

Author Comment

ID: 22696129
Figured i would include link to Asus Info page on Board. (also below is the manual for it)

Asus Product Info Page:


Expert Comment

ID: 25423098
For RAID5 and RAID6, I would use a hardware solution because its CPU intensive.

However, Windows software raid works great on RAID1 (mirroring) and RAID0(Striping).

Also, the comment that software raid sends more commands than hardware raid is NONSENSE.

Hardware raid -is- software on a chip and works the same in sending commands. The -only- benefit of hardware raid is offloading work to a dedicated CPU.

Software raid is actually easier to recover. You just take the disk to any Windows XP or higher machine that can recognize Dynamic disks.  In hardware raid you need the exact same controller
LVL 23

Expert Comment

ID: 25434782
hunter44102's  comment that  "Hardware raid -is- software on a chip and works the same in sending commands."   is basically nonsense,  and is clearly referring to fakeraid, which is not hardware RAID.

Software RAID5/6 should be avoided, due to serious reliability and performance issues;  Software RAID1  and software RAID 1+0 may be an option (in some
cases),  with the 1+0  option definitely preferred to lower the SW penalty..

In a true hardware RAID solution, hard drives plug directly into the controller, and commands are sent directly to the hard drives;  no additional commands cross the PCI bus:  in software RAID, there are always additional commands crossing the CPU bus,  it's much more than twice as many, actually.

In a software RAID1, over twice as much PCI bandwidth is required,  and over twice as many disk I/O commands cross the PCI bus and are executed by the main CPU.  Also, since the CPU must partcipate,  twice as many CPU interrupts.

CPU speed (Mhz) isn't the only issue,  more interrupts lead to more OS context switching,  and  every architecture has its limits for number of interrupts that can be executed per second;   the cost of context switching is OS-dependent.
UNIX handles this well.   Windows, not so much...
Utilizing software RAID (especially with more than 2 disks)  will  impact the interrupt capacity available on your systems.

This is acceptable on workstation type systems, and low-end server setups.
It's even easier to recover a Software RAID setup from a completely failed server, since you aren't reliant on a proprietary RAID controller  to be able to read your disks.

But on mid to high-end mission critical server setups, where you need the reliability and performance, and you have same-day warranty service on your hardware from a Tier 1 vendor such as HP or Sun (and therefore, can easily get warranty replacement within hours), hardware RAID generally provides a much better experience.

Modern CPU multi-core CPUs and  BUS architectures on modern servers typically provide a lot more processing power, interrupt capacity, and PCI bus bandwidth than you actually need for server operations,  and  Software RAID's  penalty is minimal, when that is the case.. so unless you plan to use most of the CPU power and Disk I/O capabilities you are equipping your server with, SW RAID should be acceptable from that point of view,  for  the low-end workloads.

In that case, you accept the cost tradeoff, for heavy RAID CPU usage, and much slower disk write performance  (though possibly better READ performance).

You might also choose software RAID for lab machines  and non-critical workstations,  that you   non-mission-critical things you don't need hot swap for.

Because generally, you will require a reboot after swapping a drive in a RAID1 setup  (even if your chassis has hot-swap bays)


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