Elaci0,   Stripe always means across the disks. So if it is 256k, then 256k is on each disk in the array. Doesn't matter the RAID type (IE, RAID5, RAID10, 50, 60 Files larger than the stripe; the file will be written in one stripe up to the stripe size, then the rest will be written in the next stripe, and when that one fills up on to the next. Which is why you want your stripe size to be as close to the average file size as you can get it.
by reading Dell-NSS-NFS-Storage-solution-final  at these sections  "The MD1200 has a RAID 6 (10+2) configuration that provides both a safe level of redundancy as well as optimal performance. The stripe element size (sometimes known as “chunk size”) on the RAID 6 or 60 is 512 KB"   "Small Configuration:mkfs.xfs -d su=512k,sw=10 -l size=128m /dev/sdX" Apart from the terminology "Stripe vs Strip vs chunk" I am now a little bit confused how whole stripe of data is spread across an array of disks. If the above is correct I should have a stripeSize=512KB*10=5MB where each disk has a chunk of 512KB of this data. In my PERC h740P I tried to replicate this configuration 10+2 RAID6 with 512K first and 256K later, but it seems that the whole stripe size is somehow fixed at 1MB. Or at least I am reading this value at /sys/block/sdc/queue/optimal_io_size  into my Redhat8.  Instead a combination of 64K*10=640K or 128K*10=1M are correctly reported. If this is the case, that PERC has a fixed stripe size of 1MB, how are data spread across the array then?     
PERC h740p and max stripe size