I tend to agree with Matt.
I've had several catastrophic power incidence on my server running
OpenSolaris without incident (such as a UPS gone haywire). Since ZFS
does transaction-safe reads and writes, the consistency on the disk has
an extremely low probability of getting corrupt. But there are always
two things to consider... Powering off the server this way could cause
the disks themselves to write garbage and ZFS (or any other filesystem)
won't have the opportunity to fix it. Also, there may be pending things
in the ZFS cache which won't be written. You can disable the ZFS cache,
but that will impact performance.
If it's a situation where you don't have control over the servers
(someone turns off the master switch), then I truly suggest that you put
a UPS on the server and have a daemon (nut, apsupcd, etc.) that get's
the signal that the power has been killed and shuts down the servers
gracefully.
Based upon the goals of Hammer, it looks like ZFS covers them all. It
looks like, on Hammer, you have to run a a prune/reblock on the
filesystem nightly to conserve resources. I would assume that heavily
pounding during the day will limit the effective utilization greatly.
How much overhead do you need for the prune/reblock, 10%, 20%? What
happens if there isn't enough room to run it?
You're skirting on very thin ice if you pull the plug to shut down the
servers no matter what system you use. Interestingly, there are no
specs for Hammer in the FS comparison chart. This doesn't sound like a
seasoned production filesystem which would scare me even more.
On 2/5/11 6:35 AM, Matt Wilby wrote:
On 05/02/2011 11:28, Basil Kurian wrote:
Here we are running backup servers only during business hours (web
development firm). At the end of day , Sometimes the servers are powered
off , without issuing any commands to shutdown them cleanly.
On 5 February 2011 16:45, Matt Wilby<matthewwi...@btinternet.com> wrote:
On 05/02/2011 10:53, Basil Kurian wrote:
Hi all
Currently in our company we are having a Dragonfly BSD backup server with
Hammer filesystem in it. One senior system administrator in our compay
chose
Hammer filesystem some times back, because Hammer filesystem can easily
recover in times of power failures. I 'm compelling him to move to ZFS
(on
FreeBSD or OpenIndiana). How durable is data on an ZFS pool (RAID or
mirror)
when power failure happen frequently.
Hi,
I use ZFS on my backup servers. I can't say we've ever had power
failures because they're in a datacenter, but I would invest in a decent
UPS if it's a regular occurrence. Hard drives don't generally like
having power suddenly removed.....
ZFS on OpenIndiana will give you nice features like file system
compression, dedupe, snapshots and constant checksumming of of in-use
blocks.
I've never used Hammer before, but HammerFS doesn't appear to offer
compression yet.
Just my opinion, but I'd say ZFS is more widely used than Hammer.
Matt
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I don't understand why you would ever want to shut a server down in this
way.
Can't you just setup a cron to shut them down at a certain time?
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