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diff --git a/src/Linux:RAID_Setup.adoc b/src/Linux:RAID_Setup.adoc new file mode 100644 index 0000000..e9455cc --- /dev/null +++ b/src/Linux:RAID_Setup.adoc @@ -0,0 +1,253 @@ +After fighting with the problem detailed in my Btrfs:RAID_Setup[ last +post] about this, I decided to go hunting for information about RAID 5 +implementation in btrfs. It turns out that it hasn't been completely +implemented yet. Given the status verbage on their wiki page, I'm +surprised it works at all. I suspect the wiki isn't entirely up to date +though since it does seem to work to a certain extent. I still need to +do more research to hunt this down though. + +You can find that wiki post +https://btrfs.wiki.kernel.org/index.php/Project_ideas#Raid5.2F6[here]. + +[[the-new-new-solution]] +== The NEW New Solution + +Since RAID 5/6 is not yet completely implemented in Btrfs, I need to find +another solution. Given that I still want redundancy, the only other obvious +option I thought I had here was a +http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1[RAID 1] configuration. +However, as many Google searches do, searching for something leads to something +else very interesting. In this case, my search for Linux RAID setups sent me +over to the official kernel.org +https://raid.wiki.kernel.org/index.php/Linux_Raid[RAID page], which details how +to use http://en.wikipedia.org/wiki/Mdadm[mdadm]. This might be a better option +for any RAID level, despite Btrfs support since it will detatch dependency on +the filesystem for such support. Everyone loves a layer of abstraction. + +[[setup---raid-5]] +=== Setup - RAID 5 + +Let's get the RAID array set up. + +---- +mdadm -C /dev/md0 -l raid5 -n 3 /dev/sdb1 /dev/sdc1 /dev/sdd1 +# Or the long version so that makes a little more sense... +mdadm --create /dev/md0 --level raid5 --raid-devices 3 /dev/sdb1 /dev/sdc1 /dev/sdd1 +---- + + +[[setup---raid-1]] +=== Setup - RAID 1 + +---- +mdadm -C /dev/md0 -l raid1 -n 3 /dev/sdb1 /dev/sdc1 /dev/sdd1 +# Or the long version so that makes a little more sense... +mdadm --create /dev/md0 --level raid1 --raid-devices 3 /dev/sdb1 /dev/sdc1 /dev/sdd1 +---- + + +[[what-just-happened]] +=== What Just Happened? + +[cols=",,,",options="header",] +|======================================================================= +|mdadm |-C,--create /dev/md0 |-l,--level raid5 |-n,--raid-devices 3 /dev/sdb1 /dev/sdc1 /dev/sdd1 +| +|Create a virtual block device at /dev/md0 +|Set the raid level to RAID 5 for our new device +|The number of RAID devices is 3 - /dev/sdb1, /dev/sdc1, and /dev/sdd1. +|======================================================================= + + +[[the-rest]] +=== The Rest + +We did just create a RAID array and a virtual device to map to it, but that's +all. We still need a filesystem. Given that this whole series of posts has been +about using Btrfs, we'll create one of those. You can still use whatever +filesystem you want though. + +---- +mkfs.btrfs /dev/md0 +mount /dev/md0 /mnt/home/ +---- + + +[[mounting-at-boot]] +=== Mounting at Boot + +Mounting at boot with mdadm is a tad more complicated than mounting a typical +block device. Since an array is just that, an array, it must be assembled on +each boot. Thankfully, this isn't hard to do. Simply run the following command +and it will be assembled automatically + +---- +mdadm -D --scan >> /etc/mdadm.conf +---- + +That will append your current mdadm setup to the mdadm config file in /etc/. +Once that's done, you can just add /dev/md0 (or your selected md device) to +/etc/fstab like you normally would. + + +[[simple-benchmarks]] +== Simple Benchmarks + +Here are some simple benchmarks on my RAID setup. For these I have three +1TB Western Digital Green drives with 64MB cache each. + + +[[single-drive-baseline]] +=== Single Drive Baseline + +[[ext4]] +==== Ext4 + +1GB Block Size 1M (1000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test.img bs=1M count=1000 +1000+0 records in +1000+0 records out +1048576000 bytes (1.0 GB) copied, 4.26806 s, 246 MB/s +---- + +1GB Block Size 1K (1000000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test2.img bs=1K count=1000000 +1000000+0 records in +1000000+0 records out +1024000000 bytes (1.0 GB) copied, 6.93657 s, 148 MB/s +---- + + +[[raid-5]] +=== RAID 5 + +[[btrfs]] +==== Btrfs + +1GB Block Size 1M (1000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test.img bs=1M count=1000 +1000+0 records in +1000+0 records out +1048576000 bytes (1.0 GB) copied, 3.33709 s, 314 MB/s +---- + + +1GB Block Size 1K (1000000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test2.img bs=1K count=1000000 +1000000+0 records in +1000000+0 records out +1024000000 bytes (1.0 GB) copied, 7.99295 s, 128 MB/s +---- + +[[ext4-1]] +==== Ext4 + +1GB Block Size 1M (1000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test.img bs=1M count=1000 +1000+0 records in +1000+0 records out +1048576000 bytes (1.0 GB) copied, 12.4808 s, 84.0 MB/s +---- + +1GB Block Size 1K (1000000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test2.img bs=1K count=1000000 +1000000+0 records in +1000000+0 records out +1024000000 bytes (1.0 GB) copied, 13.767 s, 74.4 MB/s +---- + +[[raid-1]] +=== RAID 1 + +[[btrfs-1]] +==== Btrfs + +1GB Block Size 1M (1000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test.img bs=1M count=1000 +1000+0 records in +1000+0 records out +1048576000 bytes (1.0 GB) copied, 3.61043 s, 290 MB/s +---- + +1GB Block Size 1K (1000000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test2.img bs=1K count=1000000 +1000000+0 records in +1000000+0 records out +1024000000 bytes (1.0 GB) copied, 9.35171 s, 109 MB/s +---- + + +[[ext4-2]] +==== Ext4 + +1GB Block Size 1M (1000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test.img bs=1M count=1000 +1000+0 records in +1000+0 records out +1048576000 bytes (1.0 GB) copied, 8.00056 s, 131 MB/s +---- + +1GB Block Size 1K (1000000 blocks) + +---- +[root@zion home]# dd if=/dev/zero of=./test2.img bs=1K count=1000000 +1000000+0 records in +1000000+0 records out +1024000000 bytes (1.0 GB) copied, 9.3704 s, 109 MB/s +---- + + +Those aren't exactly dazzling write speeds, but they're also not too bad, given +what's happening in the background and that I'm using three standard 7200 rpm +desktop drives with 64MB of cache a piece. Later down the line I might test +this with a RAID 0 to see what the max speed of these drives are (though it +should predictably be three times the current speed). + + +[[final-thoughts]] +== Final Thoughts + +My favorite thing about this at this point is the layer of abstraction doing +RAID through mdadm provides (we all know how much Linux folk love modularity). +Using the RAID functionality in Btrfs means I am tied to using that filesystem. +If I ever want to use anything else, I'm stuck unless what I want to move to +has its own implementation of RAID. However, using mdadm, I can use any +filesystem I want, whether it supports RAID or not. Additionally, the setup +wasn't too difficult either. Overall, I think (like anyone cares what I think +though) that they've done a pretty great job with this. + +Many thanks to the folks who contributed to mdadm and the Linux kernel that +runs it all (all 20,000-ish of you). I and many many other people really +appreciate the great work you do. + +With that, I'm going to sign off and continue watching my cat play with/attack +the little foil ball I just gave her. + + + +Category:Linux +Category:Btrfs +Category:Ext4 +Category:Storage +Category:RAID + + +// vim: set syntax=asciidoc: |