"warning!: only 995 of 1984 eraseblocks have valid erase counter"

[Gilles]

Hello

	After "make" built rootfs.ubifs, I ran ubinize before uploading the
file to a web server.

I then downloaded that file on a uClinux appliance, and ran the
following command to format /dev/mtd2 with the image:
=========
ubiformat /dev/mtd2 -s 512 -f rootfs.ubi.img
=========

This command triggers the following warning:
=========
...
libscan: scanning eraseblock 1982 -- 99 % complete  MTD_ioctl
MTD_read
libscan: scanning eraseblock 1983 -- 100 % complete  MTD_ioctl
MTD_read

ubiformat: 995 eraseblocks have valid erase counter, mean value is 14
ubiformat: 989 eraseblocks are supposedly empty
ubiformat: warning!: only 995 of 1984 eraseblocks have valid erase
counter
ubiformat: mean erase counter 14 will be used for the rest of
eraseblock
ubiformat: continue? (yes/no)
=========

Running just "ubiformat /dev/mtd2 -s 512" triggers the same warning.

I don't know what the warning really means, and what the consequences
are when answering "yes". Could someone tell me?

Thank you.