If this is what you are looking to do, there are two more approaches you could consider. I have used both to varying degrees of success. The first is to just keep the first part of the disk in cache. Ie. Set up the device as you want, then run the following either as a cron job or inside a 'while true' loop in the background: cat /dev/yourdevice | dd bs=1048576 count=$N of=/dev/null (replacing $N with the number of MB you want from the beginning of the drive to remain in the block device cache) This will simply periodicaly read $N MB from the beginning of your device, which keeps it in the buffer. I did this on a drive exported over ATA-over-ethernet to my windows machine as it's boot drive, and had sub-millisecond access times, very fast boot and app loading times... Although I was keeping the entire C: drive (6GB) in the buffer on my home server with 8GB ram :) The second way I have used (and replaced with the above for simplicity) is to set up an mdraid1 between the ramdisk and an equally sized partition, using the write-mostly and write-behind options, then use dmsetup (or LVM, I went for the direct approach) to concatenate it with the rest of the disk. My first way works brilliantly for me, as it is so simple yet so safe. I have even had a power cut in the past and no data was lost (although of course it forced windows to do checkdisk on boot, but it would have anyway). Hope this is helpful Mouse -----Original Message----- From: linux-lvm-bounces@redhat.com [mailto:linux-lvm-bounces@redhat.com] On Behalf Of Stuart D. Gathman Sent: 13 May 2008 02:29 To: LVM general discussion and development Subject: Re: lvm partition on ramdisk On Mon, 12 May 2008, Larry Dickson wrote: > However, let me follow up your (and Stuart's) point. Are you saying that an > unmounted LVM volume will mess up the boot, even if the volume in question > is not mapped to boot or /? I was proceeding under the assumption that LVM > would be happy to sew the pieces together again later, even if the data in > them is trashed. As long as the VG is not needed in initrd (e.g. a test VG), you should be ok. You will simply have to go through the procedure of removing the "failed" PV and adding it back after a reboot. As long as your root fs (and /usr and other stuff needed at startup) are not on the test VG, you should be fine. The problem is that the VG will not activate automatically with a missing PV. Even with --partial, it will activate the VG as readonly metadata. Yes, AIX handles this better, IMO. But Linux LVM is getting there. For your application, you should make a separate "testvg" VG for your test that does not have your system. At boot, activate the VG with --partial, then use "pvcreate -u " to set the UUID on the ramdisk to match the UUID originally on the ramdisk, followed by vgcfgrestore. -- Stuart D. Gathman <stuart@bmsi.com> Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flammis acribus addictis" - background song for a Microsoft sponsored "Where do you want to go from here?" commercial. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ This has been checked by www.blackspider.com _________________________________________________________ Zetex Semiconductors - Solutions for an analog world. http://www.zetex.com http://www.zetex.cn E-MAILS are susceptible to interference. You should not assume that the contents originated from the sender or the Zetex Group or that they have been accurately reproduced from their original form. Zetex accepts no responsibility for information, errors or omissions in this e-mail nor for its use or misuse nor for any act committed or omitted in connection with this communication. If in doubt, please verify the authenticity with the sender. _________________________________________________________ _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
