Since this is a RasPi,
/dev/mmcblk0 is probably the system disk, and so
/dev/sda is the external hard disk.
Since you erased it using a modern Mac, it got partitioned and initialized in Mac style: there is a GPT partition which defines two partitions:
/dev/sda1 is an UEFI ESP boot partition, and
/dev/sda2 is the rest of the disk initialized using a
I see the following complications:
fdisk command does not understand GPT: it apparently understands and detects only the legacy MBR partitioning scheme. So it only shows
/dev/sda1 with partition type
ee. This is a "protective dummy MBR" that is part of the GPT partition specification. Its purpose is to tell any tools and systems that only understand old-style MBR partitioning: "this device in use by something you don't know about, don't mess with it". This is why the
blkid command sees
fdisk doesn't. There may be another partitioning command
gdisk that will understand the GPT partitioning scheme. Alternatively,
parted will be able to handle both partitioning schemes.
The filesystem type
hfsplus can be used by Linux systems if the appropriate HFS filesystem tools and filesystem support kernel modules are available. They may or may not be included in your RasPi Linux distribution. Even if the tools are available, the
hfsplus filesystem type includes file owner and permission information, which may complicate the use of disks that are moved from one system to another on a regular basis. This may or may not be a problem for you.
Since the disk now has multiple partitions, whatever auto-mount system you might have might be skipping the disk as "too complex to handle automatically, let the sysadmin do it"
If you don't plan to use the external disk as an UEFI boot media, then the
/dev/sda1 partition is useless to you and you might want to remove it.
If the true size of the external hard disk is not more than 2.2 TB, and you want maximal compatibility with any computers, you might want to delete the GPT partition table. If the
gdisk command is available, its
o command can be used to clear out all the parts of a GPT partition table. Then you can use the
fdisk command to re-partition the disk in MBR style, and create just one large partition with a filesystem type that is appropriate for your use.
If the size of the disk is more than 2.2 TB, you'll want to keep using the GPT partitioning scheme, since 2.2 TB is the maximum disk size that can be handled with MBR partitioning: any capacity beyond that will be simply wasted. You might still want to use
parted to remove the Mac-created partitions from the disk and create just one partition with a filesystem type that is appropriate for your use.
Regarding the choice of filesystem type: the external disk probably had originally a FAT32 or NTFS filesystem: FAT32 is the most universally accessible, but has an maximum file size limitation of only 4 GB, which can be annoying on modern systems. NTFS would have been a good default choice for large disks in a Windows ecosystem, and most modern Linux distributions can access NTFS filesystems fairly easily. But if this external disk is to be used by this RasPi only, you might choose a filesystem type that is native to Linux.
ext4, the same filesystem type as on your system disk, is very reliable and so might be a good choice. However, Windows and Mac systems won't be able to access
ext4 filesystems without extra tools or drivers.
As you apparently have a Mac, you might even choose to keep using the
hfsplus filesystem on the external disk: it may require some extra steps to make it usable, but that would allow you to access it fairly easily with Mac if need arises.