>>>>> "nl" == Nicholas Lee <emptysa...@gmail.com> writes:
nl> zfs handles so much of what once would have been done in
nl> hardware and by drivers. While this is good, it is leaving
nl> this huge grey area where it is hard for those of us on the
nl> front line
well that's not what I meant though. The battery RAM cache's behavior
can't be determined by RTFS whether you use ZFS or not, and the
behavior matters to both ZFS users and non ZFS users. The advantage I
saw to ZFS slogs, is that you can inspect the source (and blogs about
the source) to determine lots of details about how slogs behave
including answers to the questions above. Better yet, with some skill
you can change the answers to suit yourself. This process leads to
some mix of good behavior and well-understood errata, while the other
process leads to frustration, war stories, and cargo-cult maintenance
``procedures''.
>> it's so extremely cheap
nl> That;s the big point. 10,000 USD for a 2U 12 disk 10TB raw
nl> NAS or 100,000 USD for the equalivent appliance.
here I was talking again about battery-RAM RAID-on-a-card vs. slog.
The battery-RAM is maybe a little bit less extra cost than X25E or
ACARD, like $250 instead of $500, plus it doesn't consume a drive
slot. This amount of cost edge matters to people with large clusters,
or to the rented-hardware hosting business.
If both firmware and driver for the LSI 1078 cards were open source, I
bet we could turn the RAM on the LSI cards into a slog. This would be
better than a SATA slog because it'd have full PCIe bandwidth and
low-latency to the RAM instead of just SATA. but it's all
proprietary, so I'm going with the slog. and keeping an eye on
FreeBSD, since maybe if they manage to get ZFS working well in 8.0 I
can finally get ZFS on top of proper drivers for the disk controller
card and SCSI mid-layer.
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