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I/O limitation of usb memory sticks
Hi.
I have a general question about usb memory sticks: Do usb sticks have a limitation of the amount of read/write operations during their lifetime? I would like to run an application on an usb memory stick, which would accesses the stick about every 60 seconds. Assuming that every access consists of 5 to 10 i/o operations, that would make around 10 mio. i/o operations in two years. Does an usb stick support this many accesses? Or does it have an "expiration date"? Martin |
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Previously Martin wrote:
Hi. I have a general question about usb memory sticks: Do usb sticks have a limitation of the amount of read/write operations during their lifetime? Yes. Depending on the technology you get something like 10,000 to 1,000,000 guaranteed overwrites. After that things get chancy and if you do not have automatic defect management, a single error can make the device unusable. There might be newer technologies that support more overwrites. This figures are per sector. If you e.g. use only 10% of the device, partition it into 10 partitions and automatically move your data to the next partition when you approch the overwrite limit, you get 10 times the durability. You can also test-read your files after they are written, and if you get errors, write them to a new file and keep the old one in place so it covers the defective sector. Of course there are other and more sophisticated defect managing schemes you can use, such as error correcting codes. You just need to be aware that from some point on a sector can fail. I would like to run an application on an usb memory stick, which would accesses the stick about every 60 seconds. Assuming that every access consists of 5 to 10 i/o operations, that would make around 10 mio. i/o operations in two years. Look into the datasheet of the device you plan to use. Reads are completely uncritical, it is only the writes that slowly destroy solid-state memory. One exception from this rule is battery-backed RAM. Regards, Arno -- For email address: lastname AT tik DOT ee DOT ethz DOT ch GnuPG: ID:1E25338F FP:0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F "The more corrupt the state, the more numerous the laws" - Tacitus |
#3
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In article , Arno Wagner wrote: Previously Martin wrote: Hi. I have a general question about usb memory sticks: Do usb sticks have a limitation of the amount of read/write operations during their lifetime? Yes. Depending on the technology you get something like 10,000 to 1,000,000 guaranteed overwrites. After that things get chancy and if you do not have automatic defect management, a single error can make the device unusable. There might be newer technologies that support more overwrites. This figures are per sector. If you e.g. use only 10% of the device, partition it into 10 partitions and automatically move your data to the next partition when you approch the overwrite limit, you get 10 times the durability. You can also test-read your files after they are written, and if you get errors, write them to a new file and keep the old one in place so it covers the defective sector. Of course there are other and more sophisticated defect managing schemes you can use, such as error correcting codes. You just need to be aware that from some point on a sector can fail. I would like to run an application on an usb memory stick, which would accesses the stick about every 60 seconds. Assuming that every access consists of 5 to 10 i/o operations, that would make around 10 mio. i/o operations in two years. Look into the datasheet of the device you plan to use. Reads are completely uncritical, it is only the writes that slowly destroy solid-state memory. One exception from this rule is battery-backed RAM. I was wondering about this myself. Back in the early days of removeabnle flash memory, I had an PCMCIA flash card in my HP palmtop which mimicked the ATA drive interface. The earliest/best such cards were made by Sundisk (now known as SanDisk). They came with a "wear levelling" program which was intended to be used periodically. As sectors became worn out through repetitive write operations, each write became slower. The leveller program detected this, and remapped things so that marginal sectors would not cause data corruption. As I see the proliferation of USB flash drives, or even flash storage cards (CF, XD, memory stock, SD, MMC) I wondering if such "wear levelling" is done in firmware. If not, wouldn't often-used parts of a drive partition, like the FAT or root directory, be at risk for becoming non-writeable as time went on? |
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