1src Forums - long term wear & tear of CF?

08-03-2006, 08:50 AM	#1
tomlouie Registered User Join Date: Jul 2005 Posts: 181	long term wear & tear of CF? Does anyone how more information about the wisdom of using a 4GB CF to replace the 4GB MD with respect to wear & tear on the CF memory? Namely, CF memory has a limited number (in the order of a million writes per block) of write cycles before a memory block becomes unwritable. I'm not entirely sure, but I thought I read that on the LD, dynamic heap was just a special part of the MD, not actual RAM. Therefore, if the MD was replaced with a CF, then normal day to day LD use would be writing to the CF via the dynamic heap. Any long term experiences with using CF as an operating system's main memory? I have some articles which are informative, but aren't definitive. Post about difference between dynamic heap and dbcache: http://www.1src.com/forums/showpost...13&postcount=24 Very good article about dynamic heap & dbcache: http://www.bitsnbolts.com/memshuffle.php article about flash memory: http://en.wikipedia.org/wiki/Flash_memory#Limitations article about installing winxp on flash drive: http://www.ehomeupgrade.com/forums/showthread.php?t=425 installing freebsd on flash as read/only, in order to workaround flash write limit: http://www.freebsd.org/doc/en_US.IS...icle.html#RO-FS anecdotal evidence of flash write burnout: http://hardware.slashdot.org/commen...595&pid=8249595 Thoughts? Tom Last edited by tomlouie : 08-03-2006 at 09:03 AM. Reason: added link to dbcache article

08-03-2006, 09:31 AM

SoS

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Quote:

Originally Posted by tomlouie

Does anyone how more information about the wisdom of using a 4GB CF to replace the 4GB MD with respect to wear & tear on the CF memory? Namely, CF memory has a limited number (in the order of a million writes per block) of write cycles before a memory block becomes unwritable.

I'm not entirely sure, but I thought I read that on the LD, dynamic heap was just a special part of the MD, not actual RAM. Therefore, if the MD was replaced with a CF, then normal day to day LD use would be writing to the CF via the dynamic heap.

Any long term experiences with using CF as an operating system's main memory?

I have some articles which are informative, but aren't definitive.

Post about difference between dynamic heap and dbcache:
http://www.1src.com/forums/showpost...13&postcount=24

Very good article about dynamic heap & dbcache:
http://www.bitsnbolts.com/memshuffle.php

article about flash memory:
http://en.wikipedia.org/wiki/Flash_memory#Limitations

article about installing winxp on flash drive:
http://www.ehomeupgrade.com/forums/showthread.php?t=425

installing freebsd on flash as read/only, in order to workaround flash write limit:
http://www.freebsd.org/doc/en_US.IS...icle.html#RO-FS

anecdotal evidence of flash write burnout:
http://hardware.slashdot.org/commen...595&pid=8249595

Thoughts?

Tom

dynamic heap and dbcache are real DRAM, storage RAM (ie where your apps and db's are stored) is the 64Mb HD partition...

08-04-2006, 04:38 PM	#3
tomlouie Registered User Join Date: Jul 2005 Posts: 181	Understood. My question still stands though. Since the microdrive has been replaced with a compact flash, this means that storage RAM has gone from a HD partition to a CF partition. Presumably, everytime the dbcache is flushed back to storage RAM, that means a write to the CF. The conventional wisdom is that having an OS use a CF card as swap space is a bad idea, as heavy read/write activity on a CF will shorten the CF lifespan. How heavily does the PalmOS write to the storage RAM, and should us LD MD->CF folks be concerned? Tom

08-04-2006, 05:09 PM	#4
dmitrygr Software engineer/hacker Join Date: Jan 2004 Location: Silicon Valley, CA Posts: 5,062	1. modern flash has write cyleces counted in tens of millions of times 2. modern flash uses wear leveling so all sectors are worn equally 3. NV partition is about 1/100 size of whole disk so we have 10,000,000 (writes) * 100 (diff places where it can be written to) / (606024365.25) (seconds per year) = 31.69 years so assuming all you do is turn the device on and off once a second (not even possible to do it this fast on LD) continously for 24 hours every day and EVERY time the ENTIRE nv area is rewritten (impossible as dbcache is much smaller) you would still have it last more then 31 years. so you can sleep safely at night knowing all is well __________________ Annoying me is NOT an approved way of encouraging me to produce software My software:PowerSDHC, PowerDrive, nuRom, UDMH, warpSpeed, PowerDiGi, brightnessFix, etc... Get it all here:http://www.PalmPowerups.com Last edited by dmitrygr : 08-04-2006 at 05:38 PM.*

08-04-2006, 06:59 PM	#5
mrp123 Registered User Join Date: Mar 2006 Location: New Jersey Posts: 212	Very well put, Dmitry. Right on. __________________ LifeDrive with 4 Gig CF card & 4 Gig SD card

08-04-2006, 10:27 PM	#6
archangel Next Sunday A.D. Join Date: Aug 2002 Location: San Antonio Posts: 840	Flash may not last forever, but it will probably last 4-5 times as long as microdrives used in the LDs. I would bet many other things will fail on a LD before a flash drive. __________________ My Current Gadgets: 16GB iPod Touch, PSP 2000, Nintendo DS Lite

08-04-2006, 10:35 PM

Clocker

Registered User

Join Date: Aug 2005

Posts: 71

Quote:

Originally Posted by dmitrygr

1. modern flash has write cyleces counted in tens of millions of times
2. modern flash uses wear leveling so all sectors are worn equally
3. NV partition is about 1/100 size of whole disk

so we have 10,000,000 (writes) * 100 (diff places where it can be written to) / (60*60*24*365.25) (seconds per year) = 31.69 years

so assuming all you do is turn the device on and off once a second (not even possible to do it this fast on LD) continously for 24 hours every day and EVERY time the ENTIRE nv area is rewritten (impossible as dbcache is much smaller) you would still have it last more then 31 years. so you can sleep safely at night knowing all is well

SLC flash have cycle life of 100,000.

MLC flash like Sandisk have only 10,000.

08-05-2006, 06:00 PM

tomlouie

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Quote:

Originally Posted by dmitrygr

... NV partition is about 1/100 size of whole disk ...

This assumes that the entire compact flash capacity is available for wear-leveling. If I've filled my LifeDrive volume to the brim with content, then the NV partition will wear through the same sectors of the CF.

That would knock your estimate from 31 years down to 4 months, albeit of nearly-impossible-in-real-life constant use.

Tom