Category: Computers

Useful Tidbits

I am always in need of a certain command or utility and end up searching the Internet for a solution. I’ve gotten tired of it and am starting to collect useful commands and utilities here so that I can easily find them. Of course that means anyone else can find them as well.

Mac OS Show All Files (including dot files) in Finder

defaults write com.apple.finder AppleShowAllFiles YES
Tested on version: 10.12.5 Sierra
I found this at Ian’s Blog.

A collection of Ubiquiti WAP links follows. I am a big fan of the Ubiquiti Wireless Access Points (WAP) and supporting Enterprise network systems.

Ubiquiti High Density WLAN Scenario Guide

Ubiquiti New BaseStationXG at a Concert Venue

Ubiquiti WiFi at FedEx Forum (14,000+ clients)

 

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

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.