On Thu, Apr 05, 2007 at 04:11:35AM -0400, Justin Piszcz wrote: > > > On Thu, 5 Apr 2007, Iustin Pop wrote: > > >On Wed, Apr 04, 2007 at 07:11:50PM -0400, Bill Davidsen wrote: > >>You are correct, but I think if an optimization were to be done, some > >>balance between the read time, seek time, and read size could be done. > >>Using more than one drive only makes sense when the read transfer time is > >>significantly longer than the seek time. With an aggressive readahead set > >>for the array that would happen regularly. > >> > >>It's possible, it just takes the time to do it, like many other "nice" > >>things. > > > >Maybe yes, but why optimise the single-reader case? raid1 already can > >read in parallel from the drives when multiple processes read from the > >raid1. Optimising the single reader can help in hdparm or other > >benchmark cases, but in real life I see very often the total throughput > >of a (two drive) raid1 being around two times the throughput of a single > >drive. > > > >regards, > >iustin > >- > >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 > > > > Really? I have copied a file from a SW RAID1 (5GB) and I only saw > 60MB/s not the 120MB/s the (RAID1) is capable of to the > destination (which can easily do > 160MB/s sustained read/write). Did you copy it multi-threaded? I said "*multiple-readers* show improved speed" and you said "I copied *one* file". Try copying two files in parallel. I'm doing in two xterms "cat file1 >/dev/null", "cat file2 >/dev/null" and my raid1 shows ~110 MB/s, each drive doing about half. On file only does about 60 MB/s (this is over a PCI raid controller so the max 110 MB/s is a PCI bus limitation). Iustin - 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
