Maybe he has raw drives that were in this NAS and is trying to match the layout to recover something? I know that's probably not going to work, certainly without a lot of other things going right, but its the first thing that came to mind, given his reasoning and how he stated it. On Aug 30, 2013 3:36 PM, "Stan Hoeppner" <stan@xxxxxxxxxxxxxxxxx> wrote: > > 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 -- 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
