On 23/04/2010 12:24, Edward Ned Harvey wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of thomas
Someone on this list threw out the idea a year or so ago to just setup
2 ramdisk servers, export a ramdisk from each and create a mirror slog
from them.
Isn't the whole point of a ramdisk to be fast?
And now it's going to be at the other end of an Ethernet, with TCP and ...
some additional filesystem overhead?
iSCSI over 1G or even 10G Ethernet to something on the remote side can
be very fast, faster than a 7200rpm drive and possibly faster than a 15k
rpm drive.
Or maybe it isn't Ethernet but Infiband, then we are looking at very fast.
The point of the ZFS L2ARC cache devices is to be faster than your main
pool devices. In particular the idea is to allow you to use cheaper
7200 rpm (or maybe even slower) disks rather than expensive 15k rpm
drives but to get equivalent or better performance for certain types of
workload that have traditionally been dominated by 15k rpm drives.
If you are using this as a ZFS log device then you need to be more
careful as the log device does need to persist, otherwise there is no
point in having it.
I remember many years ago on SPARCstation ELC (sun4c) systems with only
8Mb of RAM and local swap (IIRC local / but remote /usr too so a
dataless client) it was better to run some X applications remotely on
another machine (that someone else was using) than to let them swap
locally. The idea being that you had to be unlucky for both machines to
need to swap and both to swap out the same program at the same time.
That was only over 10BaseT.
What I'm saying is that this isn't new, don't assume that the path
to/from local storage is faster than networking.
--
Darren J Moffat
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
