Messages in this thread | | | From | Neil Brown <> | Date | Mon, 12 Sep 2005 10:36:31 +1000 | Subject | Re: read-from-all-disks support for RAID1? |
| |
On Monday September 12, jesper.juhl@gmail.com wrote: > > No, I don't think so. The overhead would be substantial, so people > > would be very unlikely to use it. > > There are situations where data integrity is far more important than speed. > On AIX I usually use the Mirror Write Consistency and Write Verify > options on my mirrored volumes that store data where integrity is more > important than speed. > I guess something like those options would also satisfy Lennert's > needs, but I don't know if it's currently possible with the Linux LVM > or elsewhere. > > You can read a bit about the MWC and WV options in AIX at : > http://publib.boulder.ibm.com/infocenter/pseries/index.jsp?topic=/com.ibm.aix.doc/aixbman/prftungd/diskperf2.htm
Thanks for the link.
If I understand the (fairly brief) descriptions correctly: Passive mirror-write-constancy has always been part of md/raid1 Active mirror-write-constancy is equivalent to the new bitmap-write-intent support. WV means read-after-write which we don't do, but might be useful.
However, I'm not 100% certain that WV would really be useful. Modern drives will almost certainly return a read-after-write request out of the drive's cache rather than going to the media. We would need some way to tell the drive to ignore the cache for this read. I suspect this is possible, but might not be trivial...
NeilBrown
- 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/
| |