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Neil Brown wrote: >On Monday September 5, wilco@baanhofman.nl wrote:> >>>Hi all,>>>>I have written a small patch for use with a HDD-backed ramdisk in the md >>raid1 driver. The raid1 driver usually does read balancing on the disks, >>but I feel that if it encounters a single ram disk in the array that >>should be the preferred read disk. The application of this would be for >>example a 2GB ram disk in raid1 with a 2GB partition, where the ram disk >>is used for reading and both 'disks' used for writing. >>>>Attached is a bit of code which checks for a ram-disk and sets it as >>preferred disk. It also checks if the ram disk is in sync before >>allowing the read.>> >>>>Hi,> equivalent functionality is now available in 2.6-mm and is referred > to as 'write mostly'.> If you use mdadm-2.0 and mark a device as --write-mostly, then all > read requests will go to the other device(s) if possible,. > e.g.> mdadm --create /dev/md0 --level=1 --raid-disks=2 /dev/ramdisk \ > --writemostly /dev/realdisk > > Does this suit your needs? > > You can also arrange for the write to the writemostly device to be > 'write-behind' so that the filesystem doesn't wait for the write to > complete. This can reduce write-latency (though not increase write > throughput) at a very small cost of reliability (if the RAM dies, the > disk may not be 100% up-to-date). > >NeilBrown > > > I was looking for that (but couldn't find it).. At this point I don't see why it wouldn't, if that also syncs from the partition then it's basically the same functionality, but written from a different perspective. To use it I'll have to deviate from stock linux and use a non-packaged mdadm, but that is better than applying my patch every kernel update ;-) Thanks, I'll look into it. Wilco Baan Hofman - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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