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Newer page: version 7 Last edited on Friday, May 15, 2009 8:05:16 am by AlPyat
Older page: version 5 Last edited on Tuesday, October 18, 2005 10:45:17 pm by CraigBox Revert
@@ -1,12 +1,40 @@
-Yeah, well, it was easy enough to get RAID working. Sort of. Here's the compressed notes; they'll be opaquish if you don't have some experience with Linux, but these are the 350 words I wish I'd read before starting. It might have taken me a minute to read and saved me about an hour.  
+!! mdadm: _device_ is too small: 0K  
+mdadm: /dev/sda3 is too small: 0K  
+mdadm: create aborted  
- gave me the basics: cfdisk /dev/hdb and /dev/hde to one big partition of type 'FD', copy a sample config from /usr/share/doc/raidtools* into /etc/raidtab and edit it, mkraid /dev/md0, look at /proc/mdstat to make sure RAID was active, mkfs /dev/md0, go eat dinner, remember raidstart and raidstop commands for future reference, put /dev/md0 in /etc/fstab, and mount -a. Now I had RAID. But it was resyncing very slowly! After bringing up the RAID for the first time , it will spend a few hours resyncing, which will throw off disk transfer rate measurements; you can umount /dev/md0 and use raidstop to stop it and look at /proc/mdstat.  
+Check that the /dev/sda3 special file is actually correct. If you inadvertantly screw up your mdadm command (eg giving /dev/sda3 as the first non-option argument) , then mdadm will quite happily replace your /dev/sda3 special with an md special:  
-hdparm -i showed me that one of the disks was in mdma2 mode , which was painfully slow (as shown by hdparm -t after a raidstop.) Also a little inspection showed that I did actually have a third IDE channel (praise be unto server -class motherboards). hdparm -d 1 -X udma2 /dev/hdc (it was hdc after I moved it to the new channel ) helped a lot.  
+# ls -ld /dev/sda*  
+brw-rw---- 1 root disk 8 , 0 2009-05-05 18:20 /dev/sda  
+brw-rw- --- 1 root disk 8, 1 2009-05 -05 19:14 /dev/sda1  
+brw-rw---- 1 root disk 8, 2 2009-05-05 19:19 /dev/sda2  
+brw-r--r-- 1 root root 9, 0 2009-05-05 20:06 /dev/sda3  
+To fix (obviously replacing "sda3" with whatever device you are actually having problems with ):  
+# rm /dev/sda3  
+# mknod /dev/sda3 b 8 3  
-''Very painful lesson'': make sure you set AUTOSTART="true" in /etc/default/raid2 on Debian-like systems , at least if you want your RAID to be mounted at boot time. (Otherwise maybe use noauto in /etc/fstab.) Also you might want to make sure /etc/init.d/raid2 is linked into the appropriate S28 slot in /etc/rcS.d ( and maybe K51 in /etc/rc6.d and /etc/rc0.d? Dunno if that matters .)  
+!!Migrating an existing partition to raid1  
+You can create a raid1 that is initially degraded; once all the data is on it and you are running from that , then you can add more devices to the raid1 and it will "rebuild" it in the background
-80 -pin IDE cables have smaller wires than floppy -disk cables, and are less prone to noise; they should be used with higher UDMA modes to reduce the risk of data corruption. udma2 is 30MB /sec and is all I can get safely on my machine; higher rates lose data.  
+# mdadm --create /dev/md0 --raid-devices=2 --level=raid1 /dev/sdb1 missing  
+ size=296696452K mtime=Tue May 5 19:29:00 2009  
+ mdadm: array /dev/md0 started.  
+# ( /dev/md0)  
+# (mount and cp stuff from sda1 to /dev/md0)  
+# ... (once sda1 is no longer in use, and the same size)  
+# mdadm --add /dev/md0 /dev/sda1  
+* [RAID Center-RAID Disk Space Calculator, Tools and Comparison Charts|]