On 10/20/2015 04:43 PM, Michael Torrie wrote: > On 10/20/2015 04:24 PM, Daniel Fussell wrote: >> In the past, it was best to have a UPS. That was long ago, and was >> largely because (PATA/SATA) drives would lie about completing writes. >> In which case, you disabled the write cache. Which was also something >> that should have been done if you were using any kind of software raid. >> >> Now that we have write barriers, it's a non-issue. Also having a >> battery-backed or flash-backed write cache on your raid controller was a >> non-issue (assuming your raid controller is smart enough to turn off >> each drive's write cache). > What about a home server situation with just a couple of bare drives in > a computer? Is there still a potential problem for data loss here? > > UPS are quite cheap these days, so it's cheap insurance I guess. > >
Even with a UPS you can stop a machine mid-write. I've got some xen domUs that went bat-snack crazy after an attempted distro and kernel upgrade, and I had to destroy the machines while they were somewhere in applying the journal, or mounting or something. A couple machines have a weird empty directory in lost+found I haven't been able to delete (thinks it isn't empty), but other than that, I've had no problems. The worst problem I've ever had was an 8 disk RAID-5 with a punctured RAID stripe due to a seriously flawed 6-month drive production run in the Philippine manufacturing plant (somebody used the wrong drive lubricant). I ended up with two or three different punctured stripes over about 5 months. The only reason XFS had any problems was because in the last punctured stripe event, I tried to outsmart the controller and do a full-stripe write at the failed location in question with dd, miscalculated the block address, and blew out the wrong stripe. Then I had two areas in the filesystem that weren't happy! Before that, the filesystem would continue to run as long as you didn't do anything with the punctured stripe. I finally gave up on that raid array (as the manufacture wouldn't replace all the questionable Philippine drives), restored the data from tape to a decent SAN array, and kicked the crappy drives to the curb. Yay for tape backup (even if it did take a week to restore it all). I'm still a little torqued at having to eat a bunch of SAS drives, and I will probably be gun shy with every drive I ever get from now on, but the filesystem performed admirably under the circumstances. Grazie, ;-Daniel Fussell /* PLUG: http://plug.org, #utah on irc.freenode.net Unsubscribe: http://plug.org/mailman/options/plug Don't fear the penguin. */
