PK1048

ZFS Resources / Links

I see some of the same questions come across a variety of mailing lists. Often times the questions are phrased differently, but they are essentially asking the same things over and over again. This is not a bad thing as new people are introduced to ZFS and start asking about it. I find that I am sending people to a number of links where people who know more about ZFS than I have already answered the questions. To simplify giving out all these URLs I am gathering them up here for reference in one place. Expect this list to grow as I find more good write-ups on ZFS and ZFS related topics.

These will all open in a new tab or window.

Matthew Ahrens on RAIDz stripe width

Richard Elling on MTTDL and ZFS configurations MTTDL == Mean Time To Data Loss or a relative measure of how safe your data will be

My ZFS Resilver Observations from replacing a drive in 2014

My ZFS Performance vs ZPOOL Layout results from testing I did while at a client in 2010

FreeBSD Wiki ZFS Tuning Guide FreeBSD specific, slightly dated, has some recommendations but does not fully explain them

Solaris Internals ZFS Best Practices Guide this one is very old but still has good information, even if it is Solaris specific

Solaris Internals ZFS Evil Tuning Guide this one is also very old, but still contains some very good information on how ZFS works

Loudspeaker Death ?

A local community theater I volunteer at is having trouble with the main speaker cluster. I am one of two Sound Coordinators for this company, so I get called for problems.

Some background, the main sound system consists of a flown cluster of four speaker cabinets: a Main covering the bulk of the audience, a Front Fill (FF) covering the first 4 or 5 rows, a Subwoofer (Sub), and a Stage Monitor (SM) covering the vast majority of the stage. All are ElectroVoice EVF series speakers. The Main is a 15″ 2-way, the FF is a 12″ 2-way as is the SM, all are 90 degree by 40 degree. The Sub is a single 18″ driver. The crossover and house processing is handled by a Rane RPM-88 driving QSC RMX series amps. We are not currently bi-amp’ing the Main, FF, or SM cabinets, but that is the long term plan.

The other night I get a call from the current production’s Sound Designer (who is also the A1 Mixer) and his A2 Deck Sound. They tell me that the Main has distortion compared to the FF or SM. They swap various parts and narrow the problem down to the wiring, passive crossover, or drivers in the Main. I am out of town and can’t stop by immediately.

When I get back into town I stop by on a dark night (they are having auditions for the next show in the season so I can only make noise and work on things for about an hour). I capture the following response using the test oscillator built into the Soundcraft K2 FOH desk. I am using StudioSixDigital’s Audio Tools on my iPhone 5 with the built in microphone.

Main 155 Hz.

Main 259 Hz.

Main 543 Hz.

Just look at all those harmonics!

Just to sure I am not seeing some weird room effect (as I sweep the frequency I can hear the drums in the pit getting excited) I mute the Main and run the same tests on the FF, see below.

Front Fill 543 Hz.

Front Fill 319 Hz.

Front Fill 153 Hz..

That is more like what I expect to see out of a loudspeaker in terms of harmonic content. Just to be certain the problem is with the 15″ cone and not an amp channel I test the horn in the Main.

Main 1 KHz.

Main 2KHz.

Main 4 KHz.

Main 8 KHz.

That all looks reasonable.

So I am thinking that we damaged the 15″ cone at some point. This is the first show that has noticed any issues and is the second production of this season. So something happened in the past few weeks to degrade that driver.

I will continue to update this post as we learn more. We can’t get up to the speaker until after this production closes in another week.

While I had my phone out and the FFT running I stopped in the Equipment Room and grabbed this spectrum. This is with all the gear running but the fans in the lighting dimmer packs were not running as there were no theatrical lights in use.

Equipment Room

I am really curious at the spike at 163 Hz. which is clearly audible in the room. Power line is 60 Hz. three phase, but that should get me 60/120/180 Hz., not 160.

I also sat in the middle of the house (it only seats about 250) and grabbed this spectrum of the noise floor.

House Noise Floor

ZFS Protects Data Again

One of the servers I manage is essentially a file server. There are two SSD boot devices and 16 data drives. The configuration is five 3-way mirrors plus one hot spare. At one point four of the 16 drives go offline all at once. My first thought is a controller gone bad. There are four controllers in play, the onboard with six ports and three add-in cards with four ports each. But looking at the device names they are not consecutive as would be expected of the four ports on one controller. So it must be something else and I don’t buy coincidence.

The hardware is a SuperMicro chassis with a SAS/SATA disk backplane. Looking at the backplane I can see that one of the four power connectors does not look right. The pin on the yellow lead has backed itself out of the molex shell. So I shutdown the server and remove the connector. The pin with the yellow lead falls out. I reseat the pin, making sure that it locks in place and plug it back in. I restart the server.

ZFS now sees all of it’s drives and automatically resilvers the drives with missing data. There was about 3.5 GB of data to resilver and it took about one minute. No drama, no loss of data, this is the way storage systems should work.