> Would you trust a drive that fails on write ? > What if it started to fail in the middle of writing a block ? Or it > could > write a journal entry but not the actual data, etc... ?
I wouldn't trust a drive that failed, period. But - it doesn't work that way. It works like this: In flash memory, each time you write to a block, you can detect how many more writes are possible in that block. So, it gives you the ability to predict the failure, and prevent it before it happens. Suppose (for the sake of easy numbers) each block is 512 bytes, and it is a 512M drive containing 1M blocks. What they do is to actually build 1.2M blocks inside the drive, but only tell the OS that there are 1M available. The SSD drives secretly internally remap blocks when they drop below a threshold, saving them *before* they fail. The OS doesn't know anything about it. I had some talks with people in the SSD industry yesterday, who said, due to consumer fears, they're overprovisioning and overcompensating. Their goal for now is to make SSD more reliable than spindle disks, because those fears hurt their industry. I must question whether there's any bias in that feedback, and I must question how well they succeed in delivering that stated goal, and I must question whether some usage pattern might defy their expectations. But I am somewhat reassured to know they're aware of such fears, and making efforts to minimize it. sdfdsfdsf _______________________________________________ Tech mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
