Hi, On Thu, 11 Feb 2010, Adam Nielsen wrote:
> This is perhaps off-topic too, but I have always wondered... > >> You might also want to look at getting a hardware RAID card or >> daughterboard like the PERC-6i - these will allow you to set up a >> RAID-10/50/60 that will stripe all data between two drives, giving you >> another twofold speed increase. You probably want to make sure that your >> card has battery backup if you care about your database - otherwise a >> power cut can lose cached data rather painfully, even if you have a UPS. >> If you're moderately paranoid, or your data is important, you should >> disable on-drive write caching, as these never have battery backup - but >> this will cost you some speed. (This is a software issue, though, and >> won't affect your purchased configuration.) > > I am curious as to why this type of battery-backed cache is important. > The OS would do a large amount of caching (Linux can have a disk cache > of many gigabytes) which I am sure would be far more effective than the > small caches on many RAID cards. > > Given that the OS, if configured properly, should provide the best type > of caching possible, why is it still necessary to have RAID cache and > on-drive cache? Surely these would provide no additional benefit? > > Anyway, just something I've often wondered about :-) Simple: because sudden total power loss could waste the buffer cache. The battery backuped controller cache would keep the data and write back after the next power-on (if it happens within the battery lifetime). Viele Gruesse Eberhard Moenkeberg (emoe...@gwdg.de, e...@kki.org) -- Eberhard Moenkeberg Arbeitsgruppe IT-Infrastruktur E-Mail: emoe...@gwdg.de Tel.: +49 (0)551 201-1551 ------------------------------------------------------------------------- Gesellschaft fuer wissenschaftliche Datenverarbeitung mbH Goettingen (GWDG) Am Fassberg 11, 37077 Goettingen URL: http://www.gwdg.de E-Mail: g...@gwdg.de Tel.: +49 (0)551 201-1510 Fax: +49 (0)551 201-2150 Geschaeftsfuehrer: Prof. Dr. Bernhard Neumair Aufsichtsratsvorsitzender: Dipl.-Kfm. Markus Hoppe Sitz der Gesellschaft: Goettingen Registergericht: Goettingen Handelsregister-Nr. B 598 ------------------------------------------------------------------------- _______________________________________________ Linux-PowerEdge mailing list Linux-PowerEdge@dell.com https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
