I've set up a computer in order to test the new LVM cache feature. It has a pair of 2 TB HDDs in RAID 1 configuration, and a 256 GB SSD. The setup will be used to store large VM disk images in an ext4 filesystem, to be served both locally and over NFS. Before I start I have some questions about this feature: (1) Is there a minimum recommended version of LVM or kernel to use? I currently have lvm2-2.02.106-1.fc20.x86_64, which mentions LVM cache in the lvm(8) man page. I have kernel 3.14.3-200.fc20.x86_64. (2) There is no lvmcache(7) man page in any released version of LVM2. Was this man page ever created or is lvm(8) the definitive documentation? (3) It looks as if cached LVs cannot be resized: https://www.redhat.com/archives/lvm-devel/2014-February/msg00119.html Will this be fixed in future? Is there any workaround -- perhaps removing the caching layer, resizing the original LV, then recreating the cache? I really need to be able to resize LVs :-) (4) To calculate the size of the cache metadata LV, do I really just divide by 1000, min 8 MB? It's that simple? Doesn't it depend on dm-cache block size? Or dm-cache algorithm? How can I choose block size and algorithm? (5) Is there an explicit command for flushing the cache layer back to the origin LV? (6) Is the on-disk format stable for future kernel/LVM upgrades? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org _______________________________________________ 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/
