On Tuesday 29 January 2008 05:15, Bill Davidsen <davidsen@xxxxxxx> wrote: > You may have missed the "much higher" part of the previous paragraph. > And given the reliability of modern drives, unless you have a LOT of > them you may be looking at years of degraded performance to save a few > hours of slow performance after a power fail or similar. In other words, > it's not as black and white as it seems. What is the pathological case? 1/2 or 1/3 write performance? For serious write performance of a RAID you want a NVRAM write-back cache for RAID-5 stripes, and the NVRAM cache removes the need for write-intent bitmaps. AFAIK Linux software RAID doesn't support such things and that putting filesystem journals and the write-intent bitmap blocks on NVRAM devices is the best that you could achieve. It seems that if you want the best performance for small synchronous writes (EG a mail server - which may be the most pessimal application for write-intent bitmaps) then hardware RAID is the only option. Are there plans for supporting a NVRAM write-back cache with Linux software RAID? -- russell@xxxxxxxxxxxx http://etbe.coker.com.au/ My Blog http://www.coker.com.au/sponsorship.html Sponsoring Free Software development - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
