On 8/31/2013 12:05 AM, Veedar Hokstadt wrote: > Thank you Stan. I agree with what you say. Sorry I was not more clear > about my situation. No apology necessary. Upon reflection I should have realized what you were attempting, given the oddball chunk size, and the fact there are only 3 types of email on this list--PATCH, help with creation, help with recovery. As we discussed, nobody in his/her right mind would want to create a new array with a 512B chunk, which leaves recovery. I should have caught that... > Marcus is correct I'm trying to perform a data recovery operation from > a failed Lacie box with two drives in a raid0 / chunk 512B > configuration. > > I am totally aware of the complications involved but if I can somehow > build a raid0 / chunk 512B array with mdadm using the raw Lacie dives > then I can take it from there to recover the data. > > I have used another proprietary app and I am able to see the data > using a custom chunk size of 1. So it should be doable I think. > > In looking at this more I tried to make a 512B stripe with dmsetup but > it fails. It seems that "getconf PAGE_SIZE" which is set to 4096 is > the lowest allowed stripe/chunk value. Maybe mdadm has the same size > limitation. The Linux kernel is designed around page size accesses. This includes IO. The Linux page size is 4KB. This is why all the Linux filesystems have a 4KB block size, and why md has a minimum 4KB chunk size. Most processor ISAs support other page sizes, but these are all greater than 4KB. To do what you desire with Linux md you'd have to find a Linux supported processor architecture with a 512B page size and hack a large amount of the kernel code. I don't believe anyone makes such a CPU and I doubt you want to tackle such a kernel programming job. My advice to you is to call Lacie and get a replacement board, or whatever part it is that failed, or buy a used unit identical to yours on Ebay. Or maybe they have some custom MS Windows software they'll sell you that will get the data off the drives. Given their customer base I doubt they'd have Linux software, only Windows. I think the Ebay route is the most appealing and has the highest probability of success. When you're done with it, throw it back on Ebay and get most of your money back. Good luck with this. Let us know if/when you succeed, and how you did it. P.S. It's surprising that the electronics died but the disks are fine. The vast majority of the time it's the other way round. -- Stan > Thank you for your help. -V > > On 8/30/13, Marcus Sorensen <shadowsor@xxxxxxxxx> wrote: >> 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 > -- 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
