I already bought Transcend microSD (SDHC) 8GB, but what a bad luck… my MikroTik RB433UAH v4.9 said it invalid and the size is 0 (zero), i can not do check drive, clean drive, & format drive. The CPU resources become 100% and restarted.
I just read http://wiki.mikrotik.com/wiki/Supported_Hardware#Memory_cards ,but there is no my card 
thanks,
Yudi