SanDisk Endurance White Paper

[rich]

Hi All,
Here is some information taken from the SanDisk web site. I am posting it here without permission. Hopefully they won't care...

Rich

Endurance of SanDisk FlashDisks when used in a Windows 95 or NT Environment

The following is the endurance mechanism of SanDisk memory:

Each 512 byte sector has an endurance (number of write cycles) of 300,000 cycles. (For industrial rated parts the endurance is 100,000 cycles). When the "hot count", or number of write cycles, reaches the terminal count, the sector is retired, and a new sector is provided from a pool of spares. SanDisk guarantees a minimum of 1% of the total capacity of the card in spares when it is shipped. The spare sectors are in a reserved area of memory, and is in addition to the normal specified capacity of the card. The substitution of spare sectors is automatic, and completely transparent to the user.

For example, a 175 MB card would have at least 1.75 MB in spares, which represents about 3425 sectors. (Each sector has 512 bytes).

For these parameters, there is a total of (300,000*3425+1) = 1,028,000,000 sector writes available before the device is exhausted.

Here's a sample calculation of a typical situation for a desktop computer, based on certain assumptions. The assumptions are:

1. The most used sectors are those used by the directory and the FAT tables. Each time a file is written anywhere on the memory, typically one directory sector and two sectors of FAT are updated. These will not necessarily be the same physical sectors throughout the life of the drive, but for simplicity, and to be conservative, this factor is not taken into account. The sectors used by files are written much less than the directory and FAT sectors, so the number of writes to file sectors is ignored for this simple calculation. Note that the smallest unit of disk memory in a DOS fat file system is actually a cluster rather than a sector. The number of sectors per cluster varies with the size of the drive.

2. The average number of file writes per day is 10 writes per hour for an 8 hour day, for a total of 80 writes per day. You can adjust this number to suit the application.

3. Assume a 220 MB capacity. The number of sectors per cluster is 8. There is a total of 430,080 sectors and a minimum of 4300 spare sectors.

For these parameters, there is a total of 300,000*(4300+1) = 1,290,000,000 sector writes available before the device is exhausted.

The number of sector writes per year is (80 writes per day)*(365 days per year)*(3 sectors*8 sectors/cluster per write) = 700,800.

So the life of the drive is 1,290,000,000/700,800 = 1840 years.

[h.katz]

hmmm......that "automatic reserve" must be why I got on a 128mg Sandisk CF 3-32 meg partitions and one 26.5 meg sized one.

Later....................Howard

[yakko]

Howard,

Your phenomenon is explained in the manual under "Marketing Megabytes" :o)

The spares are in addition to the marketing meg capacity of the device.

<font size=-1>[ This Message was edited by: yakko on 2002-06-11 01:49 ]</font>

[mark_c]

I wonder if anyone will be challenging SanDisk in 1840 years time if theirs fails prematurely. :-)
Somehow I think other factors will deteriorate the CF card well before then.
ie electrical spikes, static discharge, corrosion, deterioration of the plastic case, not to mention the user.

to justify my case I bought a CF card with my new Digital Camera. It broke before I got home, swapped it for the same next day, broke a week later (dumped the contents twice in a week), swapped it for a SanDisk and so far it's OK after 3 months.

look at CDs they were supposed to be good for 50-100 years weren't they ? I've had plenty die within a year. Even DVD is pretty poor, of 30ish we have bought New within the last 6 months, 3 or 4 have had to be returned with maybe one or two plays.