Am 31.12.2011 16:11, schrieb Roberto Ragusa: > On 12/31/2011 02:11 AM, Reindl Harald wrote: >>>> for better performance you could use RAID10 in the far layout instead (raid10,f2), >>>> this is a direct replacement with the enhanced raid10 driver, which gives double >>>> the sequential read speed compared to raid1. Use "--level=10 -p f2" as additional >>>> parameters when creating arrays with mdadm. >> >> hmm is there a way to change this in an existing RAID10? >> i think i would like this for / where read-performance is much >> more important and /dev/md2 is perfectly with near-layout >> for write-performance (hughe data, virtual machines) > > It is apparently impossible to change the layout from near to far. > If you think about how different they are, it is difficult to > imagine how a conversion could be done. > > The best option is to boot from a rescue image, copy the root partition > somewhere else, destroy and redo the RAID and copy the root partition back. > > In that case, you may want to consider the offset layout too. > After some experiments when making a filesystem for VM files, the best > option proved to be offset=2 with chunksize=4MiB. > Very good linear read speed, and good write performance even on random writes. > > # cat /proc/mdstat > Personalities : [raid10] > md10 : active raid10 sdd5[3] sdc5[2] sdb3[1] sda3[0] > 285196288 blocks super 1.2 4096K chunks 2 offset-copies [4/4] [UUUU] > > unused devices: <none> > # hdparm -t /dev/md10 > > /dev/md10: > Timing buffered disk reads: 922 MB in 3.02 seconds = 305.11 MB/sec OK, so better leave it as it is :-) > 200 MB/Secnod are not too bad and i considered it only if it is not too much risk, but not risk setup the machine again while there are two physical cloesn running perfect at all
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