Mailinglist Archive: opensuse (2348 mails)

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Re: [opensuse] Software IDE RAID versus hardware IDE RAID
  • From: "Jason Bailey, Sun Advocate Webmaster" <webmaster@xxxxxxxxx>
  • Date: Wed, 02 Apr 2008 11:53:00 -0600
  • Message-id: <47F3C7FC.2090104@xxxxxxxxx>
On Tue, Apr 1, 2008 at 6:48 PM, Jason Bailey, Sun Advocate Webmaster
<webmaster@xxxxxxxxx> wrote:

I've always felt software raid was too much of a tax on the system, not to
mention less reliable (regardless of OS).


Wrong on both counts.

Not so fast... just hold on there.


So wrong that merely stating that indicates you have never even used
software raid.

Not so. I have used software RAID on many systems, just not on a SUSE Linux machine. I've simply never used YaST to set it up. I have mixed feelings about software raid, regardless of platform.

You just went out and spent the money, and never looked back.


Wrong again. Boy, you're making some big conclusions here. My tech partner and I actually did quite a bit of research before coming to the same conclusion. That aside, past experiences speak volumes. You stick with what you know works - what you have had good experience with.

I manage several servers all of them loafing along at under 2%
utilization under heavy
data access traffic from a multitude of work stations. That's 2%
total system utilization
for both samba and RAID combined. Software raid is fast, and lightweight.

Linux raid is faster and more lightweight than that of Windows, at least in my experience. But it's still CPU cycles that could instead be performed by a RAID card with onboard processing. And 2% is much lower than what I have experienced. If you're going to make that argument, then I guess hardware accelerated video cards are worthless too... let's just stick with software rendered openGL from now on....


With a raid card your system never gets any faster than that card.
Beef up the server,
and its still as slow as the card. Software raid improves with each
server upgrade.

That's a stretch if I've ever seen one. Whether you're taking SATA or EIDE, you have the physical speed of the channel. A SATA1 RAID card runs at SATA1 speeds, along with the connected SATA1 channel. Same goes for SATA2 or EIDE. Upgrading operating systems won't change that. You've gotta change hardware to make that happen.


And if ever have one disk crash or a controller fail with hardware raid you have
to go find another card to match, because the remaining raid drives are recorded
using a proprietary scheme that is not transportable.

Could the card fail? Yeah. But individual drive can still be mounted as an individual drive and the data can be salvaged, if needed. Been there, done that.

Proprietary schemes? My card saves the array data on the firmware of the card, not on the hard drives in the RAID array. So I don't know what RAID cards you've been using. In any event, the raids I use aren't dependent upon kernel modules and drivers that can go awry because of the onboard processing. A physical card is less prone to software related issues that can creep up.


With software raid you can mix scsi, ide, sata drives, and actually
gain performance
by doing so. With hardware raid you are locked into a specific type
of disk, and
usually a specific SIZE of disk.


Performance gains? That's a real stretch. When the card can take away processing cycles away from your processor, the hardware raid will speed things up, not the other way around.

Now, remember... not all hardware raid cards are created equal. Some cards don't have onboard processors, which means they have to have drivers (i.e. kernel modules) to power them (the processing is done by the PC's CPU. In those cases, some of your arguments are more arguable. But I'm talking about RAID cards that have onboard processors. These are not the same beasts.

As for less reliable, I've had disks fail over time 8 years using
software raid,
but regardless of raid type (1 or 5) I've never lost any data.


Linux software raid, in my opinion, is more reliable than that of Windows (yeah, a real shocker). But I still don't think software raid can outperform our outlast hardware raid with onboard processing. I think a majority of system admins out there would agree.

And when drives did fail, recovery of the array was as simple as installing
the replacement disk (or inserting a new hot-spare). Raid rebuild happened
totally in the back ground without any down time beyond what was necessary
for the actual disk swap. In one server, with hot removable drives, a drive swap
on the fly was a total non-event. The users never knew it happened.


I have had my RAID break once. I entered the RAID card's BIOS and it was a trivial fix. I plugged the new drive in and told the BIOS to replace the bad drive in the array and wallah... it was done. RAID cards don't necessarily make additions or repair to your array more complicated. In fact one could argue that with some raid cards, it's EASIER to fix or setup than with software raid.




Whether or not to use hardware or software raid is a personal decision, and there are pros and cons to each. The biggest benefit of software raid, in my opinion, is the cost (no extra hardware to buy). But I think if reliability and performance are your priorities, hardware raid is the way to go.

But then again, obviously not everyone sees things the same way...
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