Flash requirement for IOS image

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IP

c3620-i-mz.123-26.bin

Release Date: 18/Mar/2008

Size: 8031.25 KB  (8223996 bytes)

Minimum Memory: DRAM:48 MB  Flash:32 MB

This image is only 8MB,why it requires 32MB Flash since basically Flash is used to store IOS image?

Is it true that generally I can copy an image to a Flash a little bit larger than the image?As long as I can copy it to flash,I can run it,right?

In flash requirement,I never see sizes like 24MB.Is it because the Flash requirement only has 8,16,32 and so on and those irregular sizes are not considered but I can still run a image smaller than my Flash.For example,run this image with 8MB+4MB SIMM Flash.

Thanks.

[Leo Laohoo]

Because the IOS file will decompress.

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My understanding is during boot process,the router read image from flash and decompress it into DRAM,not to the flash?

like this image

IP  c3620-i-mz.123-13b.bin Release Date: 16/Aug/2005 Size: 7538.91 KB  (7719840 bytes) Minimum Memory: DRAM:48 MB  Flash:8 MB

There's no extra space in flash for decompressing.

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from http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtwrmrbt.html

Benefits of Warm Reload

Quicker Router Reload

By eliminating the need to copy an image from flash to RAM and decompress it, the reload time of a router is reduced by 2 to four minutes. The time savings is greater on platforms that use the BOOTLDR images because tha additional step of loading a BOOTLDR image and parsing the configuration file by the BOOTLDR image can be avoided.

Flash Card Removal

The router is not useless if a flash card is removed because it can still reboot as long as it is not forced into a cold reboot (such as a power failure).

Warm Reload Functionality

When encountering a crash, a Cisco IOS image transfers control to ROMMON, which copies the system image from the storage device (which is typically flash) to main memory, decompresses the system image, and transfers control back to Cisco IOS. Warm rebooting allows the image to return to the start of the text segment in memory and restart execution from that point, thereby, eliminating ROMMON intervention. A copy of the initialized variables is kept in memory and is used to overwrite the existing memory location where the initialized variables are stored. Thus, when the CPU returns to the start of the text segment and begins operating, the information is the same as if execution had begun after the binary had been read from flash and decompressed.

Tho it's something about warm reload,it still shows when the router boots,it copy the compressed from Flash to RAM and then decompress it.So ?

[podhillo · Accepted solution]

Hi,

Flash size is recommended more than image size due to the fact that it stores vlan information and some time in many cases sdm info and GUI helper files so that we can access that perticular device through IE.

We can use the following command to push in image bigger than the flash.

squeeze

To permanently erase files tagged as "deleted" or "error" on Class A Flash file systems, use the squeeze command in EXEC mode.

squeeze [/nolog] [/quiet] filesystem:

Syntax Description

/nolog	(Optional) Disables the squeeze log (recovery data) and accelerates the squeeze process.
/quiet	(Optional) Disables status messages during the squeeze process.
filesystem:	The Flash file system, followed by a colon.

Hope this helps your queries.

Regards,

podhillo