On Mon, Jun 26, 2017 at 6:12 PM, FERNANDO FREDIANI <fernando.frediani@xxxxxxx> wrote: > Hello folks. > > I have been using Bcache in a server in production with pretty good results > so far. > > Now I am looking to add it also to another server that is suffering from > disk I/O. However this server in question has a fairly large storage running > (circa 8TB of used data) and therefore stopping it for a long period becomes > difficult. > > Question is: Can I add an SSD and Bcache to this server and use it for the > existing 8TB filesystem ? If so when I run make-bcache -B /dev/sdx1 to > create the backing device will it not overwrite what is currently on > /dev/sdx1 ? Yes you can if you are prepared to do some re-partition tricks. Maybe there is a tool/script that can do that, AFAIK there is some python prog called blocks for this. Anyhow, what make-bcache -B /dev/sdx1 does is write an 8KiB sized header at the start of /dev/sdx1. So in case this is the only GPT based partition on the diskdevice that currently starts at 512-byte-sized sector 2048, there is usually some free space between GPT table and 2048. So make sure you have all backupped, then unmount the fs and use gdisk to set the starting sector of /dev/sdx1 to 2032, by delete first and re-create (with alignment set to 16 sectors first). Then make sure the kernel uses the new partition table (partprobe or reboot) and run make-bcache -C <SSD> -B /dev/sdx1. You can now access the fs via /dev/bcache0 Some people might consider this way too risky, but I have successfully used it, also in reverse order for removal of bcache. You might have a slighty different disk setup than I assume, but I hope th eprinciple is clear. If you would script it, it takes about the time of an unmount+mount, so seconds instead of hours or even days. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
