dead slow update servers

Karl Denninger karl at
Sun Jul 14 12:23:48 UTC 2019

On 7/14/2019 00:10, hw wrote:
> "Kevin P. Neal" <kpn at> writes:
>> On Sat, Jul 13, 2019 at 05:39:51AM +0200, hw wrote:
>>> ZFS is great when you have JBODs while storage performance is
>>> irrelevant.  I do not have JBODs, and in almost all cases, storage
>>> performance is relevant.
>> Huh? Is a _properly_ _designed_ ZFS setup really slower? A raidz
>> setup of N drives gets you the performance of roughly 1 drive, but a
>> mirror gets you the write performance of a titch less than one drive
>> with the read performance of N drives. How does ZFS hurt performance?
> Performance is hurt when you have N disks and only get the performance
> of a single disk from them.

There's no free lunch.  If you want two copies of the data (or one plus
parity) you must write two copies.  The second one doesn't magically
appear.  If you think it did you were conned by something that is
cheating (e.g. said it had written something when in fact it was sitting
in a DRAM chip) and, at a bad time, you're going to discover it was

Murphy is a SOB.

> Mirroring the N disks would require another N disks, which you don't
> have.
> "Performance" isn't much better defined as "properly designed" here.  In
> practise, I prefer a hardware RAID5 with N disks over a raidz with N
> disks and a RAID10 over a RAID5.  Unfortunately, in practise, the number
> of disks is limited because they aren't cheap and because only so many
> disks can be connected to a machine without further ado while there is a
> certain requirement for storage capacity.  Reality is not proper
> designed :/
> What do you do when you put FreeBSD on a server that has a hardware RAID
> controller which doesn't do JBOD?  Use ZFS on the RAID?

Throw said controller in the trash and get a proper one.

Raid controllers were very useful a decade ago when ZFS was
trouble-ridden and the controller's firmware was less-so.  Now it's the
other way around.

And whether you do your Raid in hardware or software Raidz is Raidz.

I binned the last of the hardware RAID adapters in my production
machines roughly five years ago.  ZFS got to be faster and more-reliable
than they were.

Karl Denninger
karl at <mailto:karl at>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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