>>>>> "Ian" == Ian Pilcher <arequipeno@xxxxxxxxx> writes: Ian> On 12/18/2015 10:07 AM, John Stoffel wrote: >>> From my reading of the docs, it's clear that zodcache is lower down >> the stack than LVMcache, but higher than bcache. Ian> I would actually say that zodcache is at about the same level as Ian> bcache. The main conceptual difference is that zodcache does device Ian> probing/recognition and setup are done in userspace, where bcache does Ian> it in kernel space. (I.e. echo the device name to Ian> /sys/fs/bcache/register and the kernel looks a the device, decides Ian> what it is, etc.) I think a picture would help show this all more clearly, but I do appreciate your clarifications. I had looked at bcache myself, but the inflexibility of it didn't make me happy. I like that lvmcache allows me to dynamically remove the cache without impacting the system, except for performance. :-) >> So describinng how your setup can provide a central cache pool across >> multiple VGs would be awesome, but it's not quite clear to me that you >> can do this in reality without doing multiple layers of block devices. Ian> Currently you'll need multiple zodcache devices to create Ian> multiple VGs. It should be possible to make these devices Ian> partitionable with a udev rule that calls kpartx as appropriate. Ok, that makes sense. One other issue I have with lvmcache is that the cache LVs are in the VG, so if you're not careful, you could expand other LVs onto those PVs. I think this is a bad design myself. >> And since I'm paranoid (to a degree!) about resiliency, mirroring the >> cache devices is a critical part for me. Ian> I haven't yet tested zodcache on top of MD RAID, but I fully expect it Ian> to work. >> Also, I'm on debian, so that's another piece of documentation that's >> kinda sorta missing. Ian> What do you need beyond what's in section III-B of the README? Sorry, I must have skipped over that too quickly, I didn't see it, I'll try to take a look and see if I can spin up something. John -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
