On 7 août 09, at 02:03, Stephen Green wrote:
I used a 2GB ram disk (the machine has 12GB of RAM) and this jumped
the backup up to somewhere between 18-40MB/s, which means that I'm
only a couple of hours away from finishing my backup. This is, as
far as I can tell, magic (since I started this message nearly 10GB
of data have been transferred, when it took from 6am this morning to
get to 20GB.)
It transfer speed drops like crazy when the write to disk happens,
but it jumps right back up afterwards.
If you want to perhaps reuse the slog later (ram disks are not
preserved over reboot) write the slog volume out to disk and dump
it back in after restarting.
dd if=/dev/ramdisk/slog of=/root/slog.dd
Now my only question is: what do I do when it's done? If I reboot
and the ram disk disappears, will my tank be dead? Or will it just
continue without the slog? I realize that I'm probably totally
boned if the system crashes, so I'm copying off the stuff that I
really care about to another pool (the Mac's already been backed up
to a USB drive.)
Have I meddled in the affairs of wizards? Is ZFS subtle and quick
to anger?
You have a number of options to preserve the current state of affairs
and be able to reboot the OpenSolaris server if required.
The absolute safest bet would be the following, but the resilvering
will take a while before you'll be able to shutdown:
create a file of the same size of the ramdisk on the rpool volume
replace the ramdisk slog with the 2G file (zpool replace <poolname> /
dev/ramdisk/slog /root/slogtemp)
wait for the resilver/replacement operation to run its course
reboot
create a new ramdisk (same size, as always)
replace the file slog with the newly created ramdisk
If your machine reboots unexpectedly things are a little dicier, but
you should still be able to get things back online. If you did a dump
of the ramdisk via dd to a file it should contain the correct
signature and be recognized by ZFS. Now there will be no guarantees
to the state of the data since if there was anything actively used on
the ramdisk when it stopped you'll lose data and I'm not sure how the
pool will deal with this. But in a pinch, you should be able to
either replace the missing ramdisk device with the dd file copy of the
ramdisk (make a copy first, just in case) or mount a new ramdisk, and
dd the contents of the file back to the device and then import the pool.
Cheers,
Erik
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