<div>The purpose of the ramdisk is to emulate a battery-backed solid-state drive which is intended to do high speed, seek-free metadata IO in a file system (for instance FAT32) in which all the metadata is at the beginning. We can't afford the SSD unless we know it is going to work.</div> <div> </div> <div>We don't care if the test data survives a shutdown, only that the mapping be right.<br> </div> <div>I did try making the whole ramdisk a PV, and it choked on that too, because of "filtering". A way around all this overprotectiveness would be highly appreciated.</div> <div> </div> <div>TIA,</div> <div> </div> <div>Larry<br> </div> <div><span class="gmail_quote">On 5/12/08, <b class="gmail_sendername">Stuart D. Gathman</b> <<a href="mailto:stuart@bmsi.com">stuart@bmsi.com</a>> wrote:</span> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Mon, 12 May 2008, Larry Dickson wrote:<br><br>> I'm trying to set up a logical volume over a 256MB ramdisk and a 1TB raid<br> > array partition. My ramdisk (set up in grub.conf with ramdisk_size=262144<br>> ramdisk_blocksize=4096) fails to make a type 8e partition either in fdisk or<br>> sfdisk. The error in fdisk is<br><br>You can't and don't need to set a partition type for a ramdisk. It<br> already is a partition.<br><br>> Can anyone give me some guidance here? Is it choking on the 4K blocksize? I<br>> wanted that for efficiency, as suggested by MrMichaelWill on his blog,<br>> but his base case seems to be a file system mounted directly on the<br> > unpartitioned device, and I need LVM.<br><br>No, just as you can make a disk device like /dev/sda a PV without any<br>partition table, you don't need a partition table for a ramdisk.<br><br>HOWEVER: you REALLY REALLY don't want to mix volatile and non-volatile<br> PVs in the same volume group. When you reboot, and the ramdisk PV is<br>missing, the volume group won't activate automatically. Furthermore,<br>you could accidentally end up with real data on the ramdisk - and it goes<br> bye bye on reboot.<br><br>Let me guess - you wanted to use the ramdisk for a snapshot? Yes, some<br>other people have tried that (see the thread here a week or so ago). You will<br>be very unhappy when the system reboots and the ramdisk is missing.<br> <br>The real way to put snapshots on a ramdisk is a "temporary snapshot" -<br>a feature which could in theory be done via device-mapper, but needs<br>utility support.<br><br>If your root fs is not on the VG you are adding the ramdisk to, you<br> could probably get away with it. Add the ramdisk, snapshot, make your<br>backup, delete snapshot, reduce ramdisk from VG. If the system crashes<br>while the ramdisk is still in the VG metadata, then you'll need to manually<br> recover the VG to activate - but hopefully that will be rare.<br><br>There is also an option you could add to initrd to activate a VG even<br>with missing PVs. But that makes all LVs read-only until the VG is repaired.<br> <br>--<br> Stuart D. Gathman <<a href="mailto:stuart@bmsi.com">stuart@bmsi.com</a>><br> Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154<br>"Confutatis maledictis, flammis acribus addictis" - background song for<br> a Microsoft sponsored "Where do you want to go from here?" commercial.<br><br>_______________________________________________<br>linux-lvm mailing list<br><a href="mailto:linux-lvm@redhat.com">linux-lvm@redhat.com</a><br> <a href="https://www.redhat.com/mailman/listinfo/linux-lvm">https://www.redhat.com/mailman/listinfo/linux-lvm</a><br>read the LVM HOW-TO at <a href="http://tldp.org/HOWTO/LVM-HOWTO/">http://tldp.org/HOWTO/LVM-HOWTO/</a><br> </blockquote></div><br>