On 8/30/2013 2:32 PM, Veedar Hokstadt wrote: > Hello, > I would like to use mdadm to set up a raid0 with a 512B chunk size. > > I ask as my purpose is to mimic a raid0 config from a Lacie NAS box > that uses a 512B chunk size. Your reasoning is flawed. Why would you want to imitate a configuration that is inherently flawed? > The lowest chunk value mdadm will accpet is 4. Anything less and mdadm > gives an error "invalid chunk/rounding value" For good reason. > Is there any way to create a raid0 with a 512B chunk? First, if you're using RAID0 it absolutely must be assumed that you desire maximum speed, care nothing for redundancy, and you don't care if you lose your data when a disk fails because you have a full backup of the RAID0 filesystem. If you want speed, using RAID0 with a 512 byte chunk isn't going to achieve it. On the contrary, using such a small chunk will drop a hammer on your throughput because you're processing a much larger number of IOs per quantity of data transferred. This is extremely inefficient, and throughput drops. With RAID0 you typically want a very large chunk, the largest your drives can ingest efficiently in a single IO. I'll make an educated assumption that you plan to store media files on this array, probably DVDs/CDs, and/or use it as a DVR. In this case you want a large chunk, 512KB-1MB. However, you've stated you want to duplicate a NAS device. Consider that GbE using Rtl 81xx devices tops out at ~70-90 MBs application level throughput. Two modern drives in RAID0 with a proper chunk size can read/write at double that rate. Given this fact, why are you bothering with RAID0? You won't see any of the increased performance RAID0 can give you. In fact a single modern drive can saturate GbE. I assume you are using RAID0 simply as an inexpensive way to maximize your storage capacity. That's fine with backups or if you have the original media. If you don't, or don't want to go through the hassle of recreating your RAID0 after a disk failure and replacement, and copying all your files back to it, I suggest you use RAID1/5/6/10 instead. -- Stan -- 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
