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August 15, 2006

Software RAID-5 in SUSE Linux 10.1

by @ 6:52 am. Filed under General SUSE, SUSE Tips & Tricks

This evening, I took a few minutes to appreciate how cool SUSE Linux 10.1 is. I did a fresh text-based install on a box with three 40 Gig HDDs, creating a software RAID-5 system. I wanted to see how hard it was. With no X11 install, just purely text-based, it took me about 28 minutes total. Granted, it was a very minimalistic install, consisting of about 450 Meg, and required only Disc 1. If you need a quick server, all you need is that first disc, baby.

Here’s the quick run-down of the RAID-5. It’s a way to make sure your data doesn’t get lost. It provides redundancy for your data. You need at least 3 of the same sized partitions. I had three 40 Gig partitions. You take the number of partitions and subtract 1. That leaves me with 2. Then, you multiply that number by the size of the partitions. That is 80. The final size of my RAID is 80 Gigabytes. If one of those babies goes down, you don’t lose any data. You just throw another 40 Gig partition in there, and it rebuilds your data. Very sweet. I could tell you more about it, but I got most of my information from here.

I thought it would be cool to try out the RAID-5 software raid. I was going to use it as an RSYNC backup server. If it ends up being really stable, I might slap it in as my main web server. It’s about 48 times the machine that that one is, anyway.

Anyone have experience with this software RAID setup?

11 Responses to “Software RAID-5 in SUSE Linux 10.1”

  1. Quentin Jackson Says:

    We use RAID all the time. Software RAID can have performance issues over hardware RAID of course. I would however question the use of RAID 5 vs RAID 1 in your case. It seems to me you achieved the same amount of redundancy as RAID1 but have had to use an extra disk and probably lost performance. My understanding is that RAID 5 would be slower at writing and reading than RAID 1. So unless you need to add lots of disks it would be pretty pointless using just three. There are of course some advantages, some RAID hardware (no idea about software) will let you add a disk into a RAID array without formatting when you have run out of space. Novell’s nss file system is the only software solution I have seen achieve this with a bit of a wow factor. Also linux does have some issues with Software RAID on SATA drives with particular chipsets in certain situations that are very noticeable. I have had the misfortune of experiencing this ;}

    Of course I could have gotten something wrong somewhere, would love it if someone could point that out so I can learn from it! ;}

    Q

  2. Scott Morris Says:

    Awesome feedback, bro. Thanks for the insight.

  3. Eric Says:

    If you have 3 available disks, RAID 5 is a better choice. Using three 40 Gig drives with RAID 1, you only would have a 40 Gig array, with one drive just sitting there. With RAID 5, you total would be 80 Gig. The performance should actually be better in RAID 5 because of the striping as opposed to mirroring.

  4. Scott Morris Says:

    Right on, Eric. That is totally why I decided to do a RAID-5 with it. Thanks, bro.

  5. Blake Says:

    Ya I heard that RAID5 has better performance than RAID1 actually. Anyways, not sure if anyone will respond but I was wondering if I already had an installation on one disk, if it were possible to add 3 more for a RAID5 Software array and mount it to say /data . Would that be possible?

  6. Trey Says:

    Where I work , http://recenter.tamu.edu , we used to use RAID 5. It reads fast but writes slower because it has to parity the information when it’s written. Essentially , with 3 x SATA drives in RAID 5 , 1/3 of each drive is on another drive. So if you write something to one disk it has to be put onto a parity which is the 1/3 of that drive. Four drives, it’s 1/4 , why RAID 5 is technically better when dealing with large arrays. Now where I work we use RAID 10. In RAID 10 you can have 4 SATA drives and lose up to 2 and still lose no data. It basically is HDA + HDB striped then a mirror is made of those stripes. So it’s RAID 0+1 but most times refered to as 10. Downside to 10 is you lose 50% of your actual space. Most of our servers have 500gb x 4. Yet only can hold about 850gb each server. In the end I am doing 250 x 3 RAID 5 for my system. Doing Logical Volumes , same sets on each disk , then RAID 5 that, then put that into a Logical Group.

  7. mark Says:

    It really depends on what you are aiming for. Raid o is better for reading since you have 2 drives to read from but you don’t see any benefit for writing. Raid 5 has to write to more than one drive and you can only read from one drive. Raid 10 is the best option for performance and reliability for data…besides hard drives are very cheap these days….through in 4 1tb hard drives and use raid 10.

  8. felipe alvarez Says:

    I was unable to make RAID 1+0 with openSUSE 10.3. Everything installed well, except the initrd, it failed saying it could not write to the disk. 4 x 500GB hard drives in RAID 1+0 array (fakeRAID, as they call it, because it comes built-it with the MoBo (ASUS)). RAID 0 worked fine. I think I’m going to set a 80GB for the OS, and just RAID the 4x 500GB for storage.

    Another funny issue I had was during the partitioning. It would show me THREE raid drives (0,1, and 2) I only tried installing on “0” maybe that was the problem (???).

    RAID 5 has better performance than RAID 1. Everybody knows that (Wikipedia)

  9. Quentin Jackson Says:

    These days I want more space in my home server so have gone for 4 1TB disks RAID 5 as I need more than two disks. It works a treat, tailing /var/log/messages will give you SMART information and you can see when your disks are going to die. I wonder if there’s a better alert tool for this. Wow in two years we’ve gone from talking 40GB drives to 1TB drives! Anyone got any good ideas on how to migrate data from 4 1TB drives to 4 1.5TB drives? 🙂

  10. Quentin Jackson Says:

    Might have just answered my own question. Found a tool called mdadm. It would appear I can take each 1TB drive out one by one and replace with a 1.5TB 1 by 1. Once I have all drives replaced I could theoretically grow the whole array. Awesome!

  11. Gary Dale Says:

    Quentin: it could be a problem with the particular SATA drive you had (remember the Seagate problem?). Software RAID works great with SATA – much better than with IDE drives (better speed, no master/slave issues, potential for hot swap, etc.).

    re. migrating to 4 x 1.4T, yes, your way works fine except that in order to grow the array, you will need to unmount it in order to resize the file system. If you have hotswap capability, you could also just add another drive of the same size and grow it live.

    If you don’t have hot-swap, growing by adding another drive would still mean only having to shutdown once rather than multiple times. Basically you would be live again very quickly while replacing all the drives would mean multiple service disruptions.

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