Date: Thu, 09 Apr 2009 00:27:57 +0100 From: spellberg_robert <emailrob@emailrob.com> To: Warren Block <wblock@wonkity.com>, fbsd_questions <freebsd-questions@freebsd.org> Subject: Re: [ fbsd_quest ] file_caching and hd caches Message-ID: <49DD32FD.8080800@emailrob.com> References: <49DCE5AD.70306@emailrob.com> <alpine.BSF.2.00.0904081549590.65423@wonkity.com>
next in thread | previous in thread | raw e-mail | index | archive | help
thanks, warren [ love your dot_com, btw ] --- Warren Block wrote: > On Wed, 8 Apr 2009, spellberg_robert wrote: > >> howdy, y'all --- >> >> so, i was looking over the offerings of the on_line retailing "usual >> suspects", >> when i got to thinking: >> >> q: to what extent does freebsd cache recently_used hard_drive files ? > > > To the extent that RAM is available. > >> q: under freebsd, to what extent are >> hard_drive internal_caches and their sizes [ e. g., 2mb, 8mb, >> 16mb ] >> important ? > > > It depends on workload. > >> i am not so much looking for a history_ and theory_of_operation as >> i am looking for a "yes/no" to the question: >> >> q: should i pay up for hd_cache, if the other hd parameters are the >> same ? > > > Again, depends on workload. Also the difference in price for relatively > small differences in cache RAM on the hard drive. now that i have a handle on today's prices, the choice of retailer is very important. it also appears [ from my reading of manufacturer's literature ] that the hd internal_cache is used as a write_buffer for the benefit of the chip_set, then the drive can take its own sweet time writing to its notion of "sector"s. therefore, for a mobo that is stuffed_to_the_gills with ram [ relative to the apps that it is running ], if i read you correctly, then reads will tend to come from mobo_ram and the hd_cache is mostly a write_buffer. i suspect that the hd_cache would be more important for an os that doesn't do its own caching [ until its notion of "idle"ness occurs ]. > >> something else that i just thought up while typing this: >> >> q: are hd internal_caches non_volatile ? > > > No. not surprised. > >> id est, >> >> q: do the cache contents survive a power_cycle ? > > > No. You may want to look at SSDs. understood. > >> [ some supplementary "fyi"s: >> >> yes, i am aware that >> hd access_times are a relative "eternity" to a chip_set's hd_port. >> >> i am not thinking about ram_size and swap_size and "thrashing"; >> all of my boxen have plenty of ram. >> >> i know i have to read it in the first time. >> rather, i am thinking about opening and reading >> some file that i recently wrote and closed. > > > FreeBSD is pretty good at that. For example, reboot and start Firefox. > Then close it and start it again. understood. > > There may be ways of prioritizing what's kept in cache, although I don't > know them. not important. thanks for the thought, though. to summarize, it looks like, for freebsd, i should "get a good price from a reputable retailer on a high_quality product from a reputable manufacturer". then, i can save my worrying_time for really important subjects, like "the determination of the correct yardarm height for the hanging of pirates". > > -Warren Block * Rapid City, South Dakota USA nice part of the country, that. chicago & north western territory. rob mchenry county, illinois
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?49DD32FD.8080800>