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256GB has just been released recently I believe so prices are still very high. I might consider buying multiple 128GB SD cards.

Nevermind. Just discovered a very detailed thread that explains everything. http://www.computeraudiophile.com/f8-general-forum/my-deep-dive-media-storage-interfaces-musical-differences-heard-between-chipsets-firewire-400-800-universal-serial-bus-industry-standard-cables-connectors-and-communications-protocols-between-computers-and-electronic-devices-sata-flash-drives-sd-cards-and-network-shares-warning-may-cause-seizures-dbt-crowd-and-flat-earth-naysayers-18108/ Guess SD card it is then, since I'll be using a late 2013 rMBP with SD running off PCIe.

Currently I have my iTunes library stored on an external hard drive. Since I travel a lot I am looking for more portable solution to store my music. So I was thinking about using either a SD card or a USB drive for my higher res files. Personally I would prefer a SD card since it's more portable and I can just leave it in the SD slot. Is there anything I need to consider though? Like data transfer rate? Are there any downsides compared to a using an external hard drive? Feel free to leave some recommendations. I need at least 256 GB. Thanks.