On 26 Dec 2020 at 22:40, Jon Brase wrote: > > Actually I anticipate swap usage at about double physical RAM (for a > total memory usage of 3x physical RAM). I'm using Debian to > administer the machine (with DOS/Win95 for actual retrocomputing), > and empirically that runs well (shell only) with that amount of swap > (at least with the swap partition on a magnetic disk). If I start > XFCE, then it starts thrashing, but I don't really need a graphical > environment there. > [...] > As above, I'm not going for quite 4x RAM for swap, but the exact > numbers in the current magnetic disk configuration are 40 MiB RAM, > 80 MiB swap, and I plan to overprovision swap significantly on CF to > spread out write wear. Part of what I'm trying to figure out is what > kind of overprovisioning I'll need to get a decent lifetime for the > swap device. > 40 MB of RAM in Windows95 - that's something I once had in a Pentium 75 MHz :-) and it worked pretty well for the applications of that time. So suppose that you give it 128 MB of swap, on a 1 GB drive. That will extend the lifetime 8 times compared to a Flash drive with exactly 128 MB, if using the same NAND technology. But again it's really the cumulative number of write transactions, rather than the size of the swap file, that is inversely proportional to calendar lifetime. And again I cannot quantify this any better or absolutely.
Linux on 40 MB of RAM... there was a time this was perfectly okay, including a GUI. I believe something like RedHat 6.2 or Debian 3-4 would fly on that setup. Obviously it would have an ancient web browser and e.g. when editing photoes you might run into the limit of available RAM :-) 40 MB should actually be enough even for modern kernels to boot, but a modern user space probably wouldn't be happy, even with some lightweight WM / desktop. > > Don't be surprised to see 25 IOps or even > > less, pauses lasting a couple seconds etc. A pretty far cry from > > those ~4k IOps that you might come to expect, based on random > > read performance. > > 25 IOps doesn't sound good. How does that compare to a similar I/O > pattern on a late 90s/early 2000s magnetic disk? > I haven't seen a harddisk of that era for a decade or so, and I don't recall testing one with hddtest - but based on the average seek times quoted in the old days (12 to 16 ms), and based on the audio impression I recall, I'd say that the hard drives of that era would exceed 25 totally random IOps. Modern 7200rpm desktop SATA drives during the last 15 years can typically achieve some 75 random IOps. About 60 IOps for laptop drives. And those numbers do not grow significantly during the years, with new disk drive generations. These are unapologetic figures, with seeks genererated by /dev/urandom and "direct access" (no caching). The random seek positions alone pretty much prevent any cache from being effective :-) > Well, the absolute ideal for swap, if I could find it, would be an > IDE device that used a couple GiB of modern DRAM and initialized > itself at boot from some partitioning plan > exactly :-) > > > I actually wanted to say this: if you > > only have use for maybe 1 GB of swap, it's no problem that your > > partition can only be 2 GB, > > Actually only 512 MiB for anything DOS will be touching (or when > BIOS first sees the drive), but that won't be a problem for the > Linux swap partition once I've done the whole "trick the BIOS" > dance. > and I'd like to say that you consistently respond in a way that makes me believe that you know your trade, when it comes to partitioning and the various size boundaries - you have my thumbs up :-) Frank _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
