Richard Elling wrote:
Erik Trimble wrote:
I just looked at pricing for the higher-end MLC devices, and it looks
like I'm better off getting a single drive of 2X capacity than two
with X capacity.
Leaving aside the issue that by using 2 drives I get 2 x 3.0Gbps
SATA performance instead of 1 x 3.0Gbps, are there problems with
using two slices instead of whole-drives? That is, one slice for
Read and the other for ZIL?
My main concern is exactly how the on-drive cache would be used in a
two-slices configuration. In order to get decent performance, I
really need the on-drive cache to be used properly.
Is the on-disk cache volatile? For most SSDs I'm familiar with, the
on-disk
cache is non-volatile, so all of the rules pertaining to whole disks with
volatile write buffers are nullified.
-- richard
I'm pretty sure it is volatile. It's a single DRAM chip.
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=333&Itemid=60&limit=1&limitstart=3
(this review is specific to the OCZ Summit, but as the parts are pretty
much Samsung-standard, it's identical to several other brand's versions)
Are you sure most other SSDs have nvram as cache? I'm looking around,
and they _seem_ to be using standard DRAM, just like Hard drives... Or
maybe the SLC-based ones use nvram, and the MLC-based ones dram...
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
