Comments on: Stupid RAID tricks with EVMS and mdadm http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/ distraction in action Fri, 5 Dec 2008 09:32:17 +0000 http://wordpress.org/?v=2.5.1 By: Dave Lachapelle » Blog Archive » Converting Raid-1 to Raid-5 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-21968 Dave Lachapelle » Blog Archive » Converting Raid-1 to Raid-5 Fri, 25 Jul 2008 14:01:22 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-21968 [...] Then I stumbled across this blog entry in which a guy creates some experimental loopback devices, creates a RAID1 array and then converts [...] [...] Then I stumbled across this blog entry in which a guy creates some experimental loopback devices, creates a RAID1 array and then converts [...]

]]> By: chutz http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-21123 chutz Tue, 17 Jun 2008 02:56:55 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-21123 Dude, that's some nifty magic and it was certainly insightful. I had no idea that checksum(1 disk) = 1 disk. Anyway, it is so much easier to just create the raid 5 on two disks instead of all this trickery. The added benefit is that you can grow it online (especially with SATA disks that can also be hotplugged). http://tips.at.gg3.net/2006/12/20/raid5-on-two-disks-only/ Dude, that’s some nifty magic and it was certainly insightful. I had no idea that checksum(1 disk) = 1 disk.

Anyway, it is so much easier to just create the raid 5 on two disks instead of all this trickery. The added benefit is that you can grow it online (especially with SATA disks that can also be hotplugged).

http://tips.at.gg3.net/2006/12/20/raid5-on-two-disks-only/

]]> By: Marki http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-18361 Marki Sun, 03 Feb 2008 20:37:49 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-18361 Nice... Just one small tip which was handy when I had to recustruct LVM with failed PV (which was not mirrored). It allows you to create loopback devices bigger than your RAM. Suppose you need to simulate 160 GB HDD. You can create it in RAM even when booted from Live CD. # dd if=/dev/zero of=/dev/shm/file1 bs=1M seek=10240 count=1 This command will create a 10 GB file, which will need only 1 MB of RAM. What this command does, is create a sparse file - nothing is allocated except last 1 MB of data, so only 1 MB of RAM is used. You can then vgcfgrestore PV headers on it - and used RAM will grow only by the amount of data you write to the file. Nice… Just one small tip which was handy when I had to recustruct LVM with failed PV (which was not mirrored).
It allows you to create loopback devices bigger than your RAM. Suppose you need to simulate 160 GB HDD. You can create it in RAM even when booted from Live CD.
# dd if=/dev/zero of=/dev/shm/file1 bs=1M seek=10240 count=1

This command will create a 10 GB file, which will need only 1 MB of RAM. What this command does, is create a sparse file - nothing is allocated except last 1 MB of data, so only 1 MB of RAM is used. You can then vgcfgrestore PV headers on it - and used RAM will grow only by the amount of data you write to the file.

]]> By: Scott Wallace http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-4595 Scott Wallace Sun, 15 Apr 2007 08:15:42 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-4595 Well, I tried your RAID1 to RAID5 conversion this weekend on my home workstation and it worked a treat. I've blogged about the experience at, http://scott.wallace.sh/node/1521. I just wanted to drop you a note thanking you for making my life that little bit easier. I didn't have to reinstall my entire workstation to double my disk space! Thanks! Well, I tried your RAID1 to RAID5 conversion this weekend on my home workstation and it worked a treat.

I’ve blogged about the experience at, http://scott.wallace.sh/node/1521.

I just wanted to drop you a note thanking you for making my life that little bit easier. I didn’t have to reinstall my entire workstation to double my disk space!

Thanks!

]]>