Putting the Redundancy in RAID: RAID-1

The next type of RAID that we'll talk about is RAID-1, otherwise known as mirroring. We won't be benchmarking RAID-1 here because, for the most part, there's no performance increase or decrease. As the title of this page implies, RAID-1 is done for redundancy.

Writing to a two-drive RAID-1 array

Unlike RAID-0, there is no preprocessing done on the data before it is sent to the hard drives. Instead, with RAID-1, a duplicate of everything written to drive 0 is written to its mirror drive. The benefit of RAID-1 is that if one drive fails, you have a perfectly working backup that can take over until you have replaced the failed drive. You have effectively doubled a single hard drive's mean time between failure by using two in a RAID-1 array. You'll notice that this is the exact opposite of RAID-0, but the downside to RAID-1 is that you spend twice as much on hard drives without getting any additional capacity or performance, just reliability.

Doubling Theoretical Performance: RAID-0 The Test
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  • Insomniac - Thursday, July 1, 2004 - link

    I was wondering how RAID1 reads back data. I thought if it was smart, it would use both drives and improve performance. If that wasn't the case, I wondered if you could choose which drive it read from. That way, you could get a WD Raptor II and a low cost 80GB hard drive to pair up. You get the redundancy and speed of the Raptor for a lower cost. What about RAID5? (I know the ICH5/6 doesn't support it, but I thought there were some chipset m,akers that did. I would like to see what that brings to the mix. Given the choice right now, I'd take redundancy over performance. Maybe RAID 5 can give you both for less than 0+1.
  • Pollock - Thursday, July 1, 2004 - link

    I really wish some regular 7200 RPM drives had been used, considering someone who can afford a 74GB Raptor won't care about the costs of RAID anyway. =P Besides, to me it seems like Raptors already perform so well that it's hard to find any performance gain anyway. I was also under the impression that a lot of people with SATA drives in RAID 0 were actually getting much more noticeable performance gains; i.e. outperforming lone Raptors. Well, whatever.
  • goku21 - Thursday, July 1, 2004 - link

    I noticed that they came to the conclusion of only using 2 drives in a RAID setup, but in my expereince the more drives the supposed increase in performance. Perhaps they should revisit this with 4 Raptors in a RAID setup.
  • kuk - Thursday, July 1, 2004 - link

    Just one small thingy ... why is the manufaturer stated in the article summary "3Com/U.S. Robotics"?
  • parrybj - Thursday, July 1, 2004 - link

    While your overall disk bound throughput may be higher, seek times are sill only as fast as the slowest drive in the array. Since seek time is a more important desktop performance metric, I would think there would be very little benefit to doing this.
  • Marlin1975 - Thursday, July 1, 2004 - link

    Well the review was nice if you are thinking of running 2 raptors on a ICH5/6 SATA ports, but what about the other 99% of use that may use VIA, SiS, etc.. and/or other 7200 rpm hard drives?
  • Matthew Daws - Thursday, July 1, 2004 - link

    I'd be interested in seeing how using RAID0 with older drives, or one old drive and a newer drive, works out. If you're upgrading your motherboard, then given that RAID comes "for free", it could be a good way to save money by buying a second, smallish hard-drive, and using your old hard-drive with this new one in parallel...
  • parrybj - Thursday, July 1, 2004 - link

    Very good article. The results are not surprising. I have one comment about RAID1. While in theory it is simply a data redundancy mechanism, in practice there are performance benefits. Any good RAID1 algorithm will use read optimizations that will allow for parallellism during read requests. Thus, under the right conditions, most RAID1 arrays will achieve higher read IOPS than a single drive. Also, there may be a performance hit on writes due to the fact that writes will only be as fast as the slowest drive.
  • djm2cmu - Thursday, July 1, 2004 - link

    #4: Excellent introduction to all the common RAID levels here: http://www.acnc.com/04_01_00.html
  • nofuse - Thursday, July 1, 2004 - link

    This article doesn't seem to be up to the standards I've come to expect from Anandtech.

    It would be more fair to say "Intel's onboard RAID 0 solution offers no performance gain." I'd be interested to see results from other RAID controllers. You can't take one product and make a blanket comment like "RAID 0 is not worth it." That would be like me reviewing an NVIDIA Vanta graphics card and saying "3D acceleration is not worth it."

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