On Tuesday September 11, iusty@xxxxxxxxx wrote: > There are many questions on the mailing list about the RAID1 read > performance profile. This patch adds a new paragraph to the RAID1 > section in md.4 that details what kind of speed-up one should expect > from RAID1. > > Signed-off-by: Iustin Pop <iusty@xxxxxxxxx> > --- > this patch is against the git tree of mdadm. Thanks. This patch is now *in* the git tree of mdadm. NeilBrown > > md.4 | 7 +++++++ > 1 files changed, 7 insertions(+), 0 deletions(-) > > diff --git a/md.4 b/md.4 > index cf423cb..db39aba 100644 > --- a/md.4 > +++ b/md.4 > @@ -168,6 +168,13 @@ All devices in a RAID1 array should be the same size. If they are > not, then only the amount of space available on the smallest device is > used (any extra space on other devices is wasted). > > +Note that the read balancing done by the driver does not make the RAID1 > +performance profile be the same as for RAID0; a single stream of > +sequential input will not be accelerated (e.g. a single dd), but > +multiple sequential streams or a random workload will use more than one > +spindle. In theory, having an N-disk RAID1 will allow N sequential > +threads to read from all disks. > + > .SS RAID4 > > A RAID4 array is like a RAID0 array with an extra device for storing > -- > 1.5.3.1 > > - > 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 - 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
