Stephen, thank you for the reply! I made a drawing based on your answer: http://s21.postimg.org/kcn4q92rr/fs_and_chunk_size.png As you can see, there are two scenario described- first one where I modify f1, f2, f3 and f4 files on a file-system which does not take the RAID chunk-size into account and second scenario where ext3/ext4 file-system is aware of the RAID chunk-size. Please confirm, that I understand you correctly. Andreas, what does this "read-modify-write" behavior mean? regards, Martin On 3/8/14, Andreas Dilger <adilger@xxxxxxxxx> wrote: > The stripe and stride options do two things: > - shift block and inode bitmaps in each group to be on different disks > - align the block allocation to the stripe and stride boundaries to > avoid read-modify-write in RAID > > The first one is irrelevant if the flex_bg option is used, since it already > packs > the bitmaps together and achieves the same effect. > > The second is meaningless for RAID-1 since writes go to every disk and > there is no parity or read-modify-write for small or unaligned writes. > > Cheers, Andreas > >> On Mar 7, 2014, at 19:23, Martin T <m4rtntns@xxxxxxxxx> wrote: >> >> Andreas, >> >> why is it relevant only in case of RAID5 or RAID6? >> >> >> regards, >> Martin >> >>> On Fri, Mar 7, 2014 at 5:57 PM, Andreas Dilger <adilger@xxxxxxxxx> >>> wrote: >>> Note that stride and stripe width only make sense for RAID-5/6 arrays. >>> For RAID-1 it doesn't really matter. >>> >>> Cheers, Andreas >>> >>>> On Mar 6, 2014, at 13:46, Martin T <m4rtntns@xxxxxxxxx> wrote: >>>> >>>> Hi, >>>> >>>> I created a RAID1 array of two physical HDD's with chunk size of 64KiB >>>> under Debian "wheezy" using mdadm. As a next step, I would like to >>>> create an ext3(or ext4) file-system to this RAID1 array using mke2fs >>>> utility. According to RAID-related tutorials, I should create the >>>> file-system like this: >>>> >>>> # mkfs.ext3 -v -L myarray -m 0.5 -b 4096 -E stride=16,stripe-width=32 >>>> /dev/md0 >>>> >>>> >>>> Questions: >>>> >>>> 1) According to manual of mke2fs, value of the "stride" has to be the >>>> RAID chunk size in clusters. As I use chunk size of 64KiB, then I have >>>> to use "stride" value of 16(16*4096=65536). Why is it important for >>>> file-system to know the size of chunk used in RAID array? I know it >>>> improves the I/O performance, but why is this so? >>>> >>>> 2) If the "stride" size in my case is 16, then the "stripe_width=" is 32 >>>> because there are two drives in the array which contain the actual data. >>>> Manual page of the mke2fs explain this option as "This allows the block >>>> allocator to prevent read-modify-write of the parity in a RAID stripe if >>>> possible when the data is written.". How to understand this? What is >>>> this "read-modify-write" behavior? Could somebody explain this with an >>>> example? >>>> >>>> >>>> regards, >>>> Martin >>>> _______________________________________________ >>>> Ext3-users mailing list >>>> Ext3-users@xxxxxxxxxx >>>> https://www.redhat.com/mailman/listinfo/ext3-users > _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
