RAID 5 Sucks on Intel Matrix ICH8 (82801 SATA RAID) Integrated Controller

I started using RAID 1 as a matter of course after suffering some major downtime due to hard drive failures on my desktop and home machines a long time ago. First, I used the software RAID available in Windows NT (or was it WIN2K?). As I started building machines with integrated (fake raid, as some people call it) RAID controllers, I took advantage of them instead of using software RAID which was, in my experience, susceptible to frequent rebuilds due to lock-ups and power outages.

In the last machine I built, I decided to give RAID 5 a try, mainly because the 320Gb drives were so cheap at that time (but I didn’t want to buy 4 or larger ones I guess?). I develop on this machine, so write performance is very important. I’ve been running RAID 5 for the last 10 months or so. I’ve never been particularly happy with the performance of this machine. It always spent a lot time hammering the hard drives and I noticed that things would get sluggish, even though my CPU utilization never cracked 5 or 10 percent.

Things finally came to a head when the family and I went snowboarding for spring break. I really wanted an offsite backup of two of my machines in case someone broke into our house and stole the computers. One is my development machine (RAID 5) and the other is our household server for photos, music, and movies (RAID 1) which also doubles as the second gaming machine for my son’s friends, believe it or not.

I had forgotten that I used RAID 5 on my development machine. I ran up to Best Buy and picked up two hard drives that I was planning to exchange with the existing hard drives in the machines. The existing HDs I removed would be my instant offsite backups. On the machine running RAID 1, this worked beautifully. On the machine running RAID 5, it obviously didn’t work at all. Since this was the morning before we were leaving, I barely had time to copy important files from my development machine to my laptop, which was coming with us and would serve as an offsite backup of sorts.

When we got back from vacation, I wanted to salvage the money I spent on the extra drive for the machine using RAID 5. I disconnected one of the drives in the RAID 5 array as the first step in trying to migrate to some different configuration. When I reattached it, my machine was unusable for 22 hours! I mean so slow it was truly unusable! Turns out, RAID 5 suffers up to 80% performance degradation when rebuilding. You can see the gory details here. Not only that, but on the ICH8 controller, you can’t migrate from RAID 5 to any other configuration. I even tried turning on array write caching to boost performance. This helped a little but be prepared for that hideous rebuild every time you hit the reset button or suffer a power outage.

Now here’s where I really saw how badly RAID 5 sucks. I still had the 500GB hd I bought that I was going to use to mirror my dev machine to. So I swapped that in to my household server machine’s RAID 1 array which had only 2Gb free (my wife takes an insane number of photos). 20 minutes later, the array is already rebuilt. Not only that, but the machine is actually usable while the array is rebuilt. I then bought a second 500Gb drive, swapped that in, and, viola — I had just increased the capacity of my household file server in less than an hour with no pain whatsoever.

Meanwhile, my dev machine is still on RAID 5. I do some research and realize that RAID 5 suffers from really bad write performance. Combine that with the fact that it’s literally unusable (at least on ICH8) while a rebuild is underway and it’s only advantage is space effeciency, and you must conclude that RAID 5 on the ICH8 (82801 SATA RAID) is a terrible choice for a development machine.

Now, how in the world do you recover from your horrible choice of RAID 5 on ICH8 without doing a complete reinstall (which is incredibly painful)? Not easily! Since I had RAID 5, the array was larger than the the individual drives that made up the array so you can’t just take a drive out of the array and copy over to it. So now you need to shrink an NTFS partition, assuming your usage of the array, like mine, is still less than the size of component drives.

If you weren’t using RAID 5, shrinking your partition would be free and easy using Ubuntu 7.1. Unfortunately, even if you go to the trouble of trying dmraid, it doesn’t work with RAID 5. After hours of research, I finally ended up buying Acronis Disk Director which worked perfectly. I was able to shrink my partition down to 200GB and then copy it to another drive.

Since I now had 6 320GB drives, I converted my newly liberated 200GB Windows XP NTFS active partition to a RAID 10 array. Just in the time it took me to write this post, the rebuild is already 40% complete and the machine has been completely usable during that time.

In conclusion, RAID 5 on the IC8H SUCKS!!! Don’t use it under any circumstances. Disk space is so cheap there’s no reason to use RAID 5 instead of RAID 1 or RAID 10 on a workstation. Either buy one more drive (RAID 10) or buy two bigger drives (RAID 1).


10 Responses to “RAID 5 Sucks on Intel Matrix ICH8 (82801 SATA RAID) Integrated Controller”

  1. Tom Says:

    Hm … I’m trying to get raid 5 going, but from the dos window thing, I only see raid 1 or 0 as options, no 5?!

  2. Kelvekar Says:

    True, I am getting rid of RAID5 on IC8H as I type. Had OEM Vista on that box, poor Vista, it got all the blame! Aw, will go with Ubuntu now for some fresh air…

  3. Alex Says:

    I have had Intel RAID 5 since Fall 2005, and I can confirm that RAID 5 rebuilds are excruciatingly slow. And for me it’s also a dev workstation. Over the years I’ve learned to pamper it so as to avoid the rebuilds from happening. For example, I have the workstation on an uninterruptible power supply unit. I also have turned off the Windows Indexing Service, which doesn’t shutdown gracefully at Windows shutdown, and often causes the RAID 5 to become corrupted, which triggers a rebuild. Etc.

    Thanks for the information regarding the RAID 1 configuration. I am building a new workstation now, and am planning to do a RAID 1 instead of 2 disks that are 1.5 TB each.

  4. Vic Says:

    What is the best way to move from RAID 5 to RAID 1. Currently configured with RAID 5 (integrated) with 3 500GB drives. I want to move to the Embeded RAID 1 with 2 1TB drives. Is this possible. What method of restore/copy is recommended to move to the new, larger drives RAID 1?

  5. jopincar Says:

    If you have less than 500GB, you can do what I did and buy a fourth drive, move the data over, then delete the raid 5 array, and build raid 10 from the four drives.

  6. steve erickson Says:

    I’m in install phase with Intel raid 5. I confirm it is terrible. One drive was marked offline so access speed was incredibly slow. So I am now rebuilding. It’s super slow and the 4 500 gig drives look it’ll take a day to rebuild. I started 6 hours ago and it’s only 7% done!
    Since I’ve got the 2008 R2 backed up on internal backup drive I should be able to resore the O/S. I hope!

    • Xya Says:

      I’am currently running a RAID5 array on an Intel ICH8. My motherboard is three years old now…

      RAID5 is slow yes, hdtach shows a 100MB/s of speed average!
      I use it only for datas so it’s okay, I had to replace one disk (of 2TB), it took 59hours to rebuild but datas were still usable not as slow as mentioned.

      System runs on a RAID0 array on same chipset, average is good, 240MB/s!

  7. DZimmermann Says:

    RAID 1 is great for redundancy, not so great for performance. RAID 0 is great for performance but not redundant. Here are a few reasons to use RAID 5:

    PERFORMANCE: First, in a minimum three-drive configuration, it’s performance is between RAID 0 and 1, yet you get redundancy. In fact, the more drives in a RAID 5 array, the faster it gets. The chances of a drive head being in the right place at the right time increases with the number of spindles, particularly with smart RAID controllers and NCQ which can read the data out of order, and even predict future reads so heads must travel less to retrieve the needed data. RAID 5 isn’t a panacea, however, because the parity calculation does take time.

    RELIABILITY: If each drive has 100K hour MTBF, four drives have an MTBF of 25K hours. WIth RAID 5, the 3 drives have an MTBF of 33.3K hours, a 33% increase in reliability over the same capacity RAID 1. There are also other side effects such as 33% less heat to exhaust from the machine, 33% less power used, and of course, more bays available should you need to expand capacity.

    EFFICIENT USE OF DRIVE SPACE: The total available space in a RAID 1 is 1/2 * disk capacity, because every byte is written on both disks. Total available space in a RAID 5 is (n-1) * size of disks used. For example, I have a lot of video and photos, and need massive space. To get 4TB of space in RAID 1 I would need (4) 2TB drives, but to get 4TB of space in RAID 5, I need only (3) 2TB drives.

    LARGE CAPACITIES: RAID 5 is useful is for making really big GPT partitions, which are helpful if you’re working with immense quantities of video, digital audio, or high resolution photography. With mirrored drives, you can’t make a partition larger than a single drive unless you’re using RAID 10 and using many more drives.

    • DZimmermann Says:

      I should also add that it is true the performance of a degraded RAID 1 is unchanged while a RAID 5 is way slower. Also, if two drives fail in a RAID 5, you’re screwed – same as RAID 1. MTBF is also important only if you’re not going to be around to replace drives that fail, but if you ahve 4/3 as many drives, statisticaly speaking, you’ll be replacing a failed one 4/3 as often. As heat is the arch nemesis of hard drives, fewer means cooler, and therefore higher reliability as well.

    • jopincar Says:

      Please note the full title of this post — are you recommending RAID 5 on the Matrix ICH8?

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