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We Get Letters Sept/Oct 2018 SEE TEXT ONLY WeGetletters by Michael W Lucas letters@ freebsdjournal.org tmpfs, or be careful to monitor tmpfs space use. Hey, FJ Letters Dude, Not that you’ll configure your monitoring system Which filesystem should I use? to watch tmpfs, because it’s temporary. And no matter what, one day you’ll forget —FreeBSD Newbie that you used memory space as a filesystem. You’ll stash something vital in that temporary space, then reboot. And get really annoyed Dear FreeBSD Newbie, when that vital data vanishes into the ether. First off, welcome to FreeBSD. The wider com- Some other filesystems aren’t actively terrible. munity is glad to help you. The device filesystem devfs(5) provides device Second, please let me know who told you to nodes. Filesystems that can’t store user data are start off by writing me. I need to properly… the best filesystems. But then some clever sysad- “thank” them. min decides to hack on /etc/devfs.rules to Filesystems? Sure, let’s talk filesystems. change the standard device nodes for their spe- Discussing which filesystem is the worst is like cial application, or /etc/devd.conf to create or debating the merits of two-handed swords as reconfigure device nodes, and the whole system compared to lumberjack-grade chainsaws and goes down the tubes. industrial tulip presses. While every one of them Speaking of clever sysadmins, now and then has perfectly legitimate uses, in the hands of the people decide that they want to optimize disk novice they’re far more likely to maim everyone space or cut down how many copies of a file involved. It doesn’t matter what operating sys- they need to maintain by reusing a partition or tem you use: FreeBSD, any BSD, Linux, dataset elsewhere on the system. FreeBSD’s Windows, illumos, whatever. Filesystems are the nullfs(5) lets you mount a partition multiple literal worst. times, essentially recycling the same chunk of I mean, let’s look at memory filesystems. The disk space. Folks who use a bunch of jails use base idea, taking a chunk of memory and using read-only nullfs mounts to have a single FreeBSD it for temporary storage, seems sound enough. base install support multiple jails. Most non-virtual computers these days have FreeBSD’s unionfs(5) lets you merge multiple more than enough memory that they can blow filesystems. Many people successfully use union- a few gigabytes for a speedy /tmp or perhaps fs to provide custom views of a filesystem, again even compiler scratch space. Configuring for jails. Unionfs is perhaps the least popular poudriere to use memory for temporary files will filesystem in the FreeBSD ecosystem though. I vastly accelerate your package builds. know several developers who won’t go near it. But FreeBSD has two different memory filesys- I know others who say it’s perfectly safe. All I tems, mfs(5) and tmpfs(5). Old-fashioned MFS know is, backups are good. blats a UFS filesystem down on top of a chunk Network filesystems? Oh please. A dedicated of memory. It’s fast, sure. But any space MFS 6GB/s SATA controller is always going to outper- uses is unavailable for other use as long as the form anything that runs over gigabit Ethernet, filesystem exists. Suppose you create a 5 GB especially if you’re using that same network /tmp with MFS, copy 4.9 GB to it, and erase it. interface to manage the host on. Yes, six gig is That 4.9 GB is still tied up. You can instruct MFS more than one gig—but that comparison also to free unused memory by enabling TRIM with has bits versus bytes. You’re looking at a 48-fold tunefs(8), but nobody bothers with that. difference in optimal throughput. And always The newer alternative, tmpfs, is specifically remember that not all network switches are cre- designed for temporary filesystems. A default ated equal. I have a whole stack of so-called tmpfs has a maximum size equal to the system “gigabit” switches that utterly refuse to pass memory plus the system’s swap space. “How more than a quarter gigabit a second. much memory do you have? Give it to me.” Be I must unwillingly concede that FreeBSD’s new sure to specify the size= flag when you create a 28 FreeBSD Journal iSCSI stack is rock solid. And FreeBSD’s NFS imple- though, I must say: at least they’re not EXTFS. mentation is among the best in the world. Many Although FreeBSD supports extfs(5) as well, so people use these in high-performance applica- that’s not much help. tions… but they’re still networked filesystems. Really, the only smart move with filesystems is These people battering them in production have not to play. top-notch network cards and switches that live up to the hype. If you ask on the mailing lists or FJ Letters Dude, forums, they’ll offer their advice. I meant, I’m looking at the installer and it FreeBSD has excellent support for the new NFSv4 protocol. While earlier versions of NFS inter- wants to know if I want to use UFS or ZFS? operate pretty well and have identical behavior, And George Neville-Neil said you needed NFSv4 is a whole different beast with different letters. semantics. You really need to do some reading —FreeBSD Newbie before deploying it. NFSv4 does have an extensive access control list system that lets you perfectly implement the worst abominations a large corpo- Oh! ration’s IT department can dream up, so that’s Use ZFS, unless you can’t. something. As a new user, don’t use ZFS on systems with You’ll occasionally see mentions of the process less than two GB of RAM. Four GB or more would filesystem, procfs(5). Many FreeBSD developers be wiser. Don’t use ZFS on non-64-bit platforms. really, really don’t want procfs to exist. When I Some virtualization systems don’t properly label documented a need for procfs in the 2018 version disk images during migration from one host to of Absolute FreeBSD, technical reviewer John another. ZFS pools migrated on such systems Baldwin rewrote ps(1) to make procfs unnecessary. won’t boot. If you’re running on a virtualization As far as I can tell, the quickest way to goad a platform, test migration on a ZFS host before FreeBSD developer into action is to need /proc. deploying it everywhere. Autofs(5) was written for desktop users. It auto- And thanks for the tip. Next time I run into matically identifies filesystems and mounts them GNN, we’ll discuss his unfortunate tendency to for you. If you enable autofs and plug in a USB encourage people. drive, the various partitions and labels on the drive will appear as directories in /media. Going into one Michael W Lucas (https://mwl.io) is the of those directories will automatically mount that author of too many books, including Absolute partition. Similarly, autofs makes NFS mount points FreeBSD, FreeBSD Mastery: Specialty available in /net. Listing the contents of /net/file- Filesystems, and git commit murder. server displays all the NFS mount points on the Send your questions to letters@ host fileserver, and going into one of those direc- freebsdjournal.com. Letters will be answered tories automatically mounts the share. It’s still in the order in which they amuse, annoy, or using a networked filesystem though, so it’ll inspire the columnist, and may be edited for almost certainly end in tears. In the defense of all of FreeBSD’s filesystems, his own purposes. Advertise ® with Us! Contact [email protected] Sept/Oct 2018 29.
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