FLASH drives do need a scheduler policy [LWN.net]

FLASH drives do need a scheduler policy

Posted Oct 1, 2004 0:45 UTC (Fri) by dmaxwell (guest, #14010)
In reply to: FLASH drives do need a scheduler policy by axboe
Parent article: Modular, switchable I/O schedulers

Technically that is true. However, the "killer app" for memory sticks is physically moving data from one system to another. Oftentimes, the systems are running different platforms. My stick can go from a Mac running OS 9 to Windows 2000 to Linux all in one day. My stick would be useless if I used a filesystem "aware of flash memory limitations". The BSDs and Linux offer an embarrassment of riches in filesystems. We can tailor filesystems to the job at hand; imagine that! If you want to move media between platforms then only one filesystem suffices regardless of it's (many) flaws.

I have to use FAT32 if I want to employ my stick as a universal device.

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FLASH drives do need a scheduler policy

Posted Oct 1, 2004 6:29 UTC (Fri) by axboe (subscriber, #904) [Link]

It still doesn't change the fact that you cannot solve this problem at the block layer, as you don't have enough information to do so - all you get is a start offset and length of where to write the data. If you get writes for the same blocks every few seconds, you must look elsewhere to fix it.

And FAT32 is fine to use on a flash stick.

FLASH drives do need a scheduler policy

Posted Oct 1, 2004 16:51 UTC (Fri) by BrucePerens (guest, #2510) [Link]

Jens,

Yes, that's true. However, it can be fixed, if the filesystem communicates either a write barrier (write this block before any blocks I send down after it) or ordering information (write block X before block Y, order of block Z doesn't matter). Once it is so easy to work on I/O scheduling, the need for this will become so evident that there is no question that it will be done.

Bruce

FLASH drives do need a scheduler policy

Posted Oct 3, 2004 9:48 UTC (Sun) by axboe (subscriber, #904) [Link]

Bruce,

We already have write barriers, and it doesn't solve the entire problem. It will make any given fs more flash friendly indeed, but it's still quite a bit away from a fs specifically designed to minimize drive wear.

Your last sentence doesn't make sense.

Jens

FLASH drives do need a scheduler policy

Posted Oct 3, 2004 12:06 UTC (Sun) by BrucePerens (guest, #2510) [Link]

Jens,

OK. I think one of the BSDs goes a bit further than write barriers in communicating time information. But I see your point that this can not go all of the way in reducing FLASH wear.

Thanks

Bruce