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 Sat, 13 Feb 2010 18:58:15 -0800 http://wordpress.org/?v=2.8.6 hourly 1 By: Converting RAID1 to RAID5 with no data loss « scott:// http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-32653 Converting RAID1 to RAID5 with no data loss « scott:// Fri, 29 Jan 2010 20:19:50 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-32653 [...] 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: Buddy Butterfly http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-28147 Buddy Butterfly Sat, 25 Jul 2009 19:17:56 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-28147 Just wanted to test it but... The f.. LVM sits on top of it and I do not have a spare disk at hand. I am not able to stop the raid device because LVM holds it. What I need is the functionality of LVM OLR but that seems not to be possible with linux lvm. Is there any chance to remove a device from a volume group with keeping all data and LVs intact such that it can be readded? Maybe someone has an hint. Chears, Buddy Just wanted to test it but… The f.. LVM sits on top of it and I do not have a spare disk at hand. I am not able to stop the raid device because LVM holds it. What I need is the functionality of LVM OLR but that seems not to be possible with linux lvm. Is there any chance to remove a device from a volume group with keeping all data and LVs intact such that it can be readded? Maybe someone has an hint.

Chears, Buddy

]]> By: n8 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-28117 n8 Fri, 24 Jul 2009 17:33:42 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-28117 I'm really not an expert at this at all, so I'm not going to guess. :) I’m really not an expert at this at all, so I’m not going to guess. :)

]]> By: Buddy Butterfly http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-28116 Buddy Butterfly Fri, 24 Jul 2009 17:02:52 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-28116 Tested it with the images and the loop devices. The reverse procedure also works! Same complaints from mdadm but no probs when confirming with yes. Before going on to the real system. Do you think there will be a noticeable performance gain in I/O when reverting back to raid1? On top of raid I have LVM. I could already gain a heavy performance increase via converting the the virtual machine images to "raw" format. This gives a real performance boost. There is a huge performance loss when using standard virtual image format on top of LVM. Tested it with the images and the loop devices. The reverse procedure also works! Same complaints from mdadm but no probs when confirming with yes. Before going on to the real system. Do you think there will be a noticeable performance gain in I/O when reverting back to raid1? On top of raid I have LVM. I could already gain a heavy performance increase via converting the the virtual machine images to “raw” format. This gives a real performance boost. There is a huge performance loss when using standard virtual image format on top of LVM.

]]> By: n8 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-28101 n8 Thu, 23 Jul 2009 22:28:29 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-28101 It seems like you ought to be able to reverse the procedure, but I've never tried it. I'd recommend trying it on disk images first like I did in the article. It seems like you ought to be able to reverse the procedure, but I’ve never tried it. I’d recommend trying it on disk images first like I did in the article.

]]> By: Buddy Butterfly http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/comment-page-1/#comment-28100 Buddy Butterfly Thu, 23 Jul 2009 21:37:39 +0000 http://www.n8gray.org/blog/2006/09/05/stupid-raid-tricks-with-evms-and-mdadm/#comment-28100 Great artikel. I wonder if it would be possible to revert the procedure. I have 2 disks running in raid5 as you converted it to. It's used in a Xen System which has a quite slow i/o performance. Now I want to try to convert back to raid1. As I understood this should also be possible with a similar procedure? I hope to get some more i/o performance. Chears, Buddy Great artikel.
I wonder if it would be possible to revert the procedure. I have 2 disks running in raid5 as you converted it to. It’s used in a Xen System which has a quite slow i/o performance. Now I want to try to convert back to raid1. As I understood this should also be possible with a similar procedure? I hope to get some more i/o performance.

Chears, Buddy

]]> 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-page-1/#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-page-1/#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-page-1/#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-page-1/#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!

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