Hi I'm using a Bunch auf HDDs in USB-Enclosures for storing files. (currently 38 HDD, with a total capacity of 9,5 TB of which 8,5 TB is used) After i realised about a year(!) ago that the files copied to the HDDs sometimes aren't identical to the "original"-files i changed my procedured so that each file is MD5 before and after and deleted/copied again if an error is detected. My averate file size is about 1GB with files from about 400MB to 5000MB I estimate the average error-rate at about one damaged file in about 10GB of data. I'm not sure and haven't checked if the files are wrongly written or "only" wrongly read back as i delete the defective files and copy them again. Today i copied a few files back and checked them against the stored MD5 sums and 5 files of 86 (each about 700 MB) had errors. So i copied the 5 files again. 4 of the files were OK after that and coping the last file the third time also resulted in the correct MD5. This time i kept the defective files and used "vbindiff" to show me the difference. Strangly in EVERY case the difference is a single bit in a sequence of "0xff"-Bytes inside a block of varing bit-values that changed a "0xff" into a "0xf7". Also interesting is that each error is at a 0xXXXXXXX5-Position Attached is a file with 5 of the 6 differences named 1-5. Of each of the 5 2x3 lines-blocks the first 3 lines are the original the following 3 lines contain the error in the middle row 6th value. NEVER did i see any messages in syslog regarding erros or an aborting program due to errors passed down from the kernel or something like that. Data for the computer/software: Hardware: Computer is a Dual P3-933Mhz with 3GB (ECC) SD-RAM, Severworks HE-SL-Chipset Source-HDD is a 200GB S-ATA device connected to a Promise TX-4 using libata. Destination-HDDs: Several different models in several different enclosures and different chipsets, mostly Genesys Logic) USB-controller: Currently i use a EHCI/OHCI-NEC-Chipset add-on card but since about 4-5 month ago i used a EHCI/UHCI-VIA-Chipset add-on card with same results. Software: Kernel: up to 2.6.18, self compiled vanilla kernels. I haven't tried 2.6.19 and i don't expect any changes from it. Distribution: Debian SID I you need any other information i will provide them as good as i can. Bis denn -- Real Programmers consider "what you see is what you get" to be just as bad a concept in Text Editors as it is in women. No, the Real Programmer wants a "you asked for it, you got it" text editor -- complicated, cryptic, powerful, unforgiving, dangerous.