Zumo User Forums

For my Zumo 396,
can I format a new 128 GB SD card and format it FAT32 with Allocation Unit Size: 65536 ?

If FAT32 it should work ...

I've never had any luck formatting a card and then inserting it. For the last few, I installed it new and let the unit format it. Dunno if the 396 will do that but the 595 and XT1 do.

FWIW, I have a 64 GB card in my XT, formatted FAT32 of course. I don't recall what I did for allocation units but I know I would have chosen significantly smaller than 65536 if I had the choice. An exFAT format would default to 8096 which would be my choice for FAT32 although if I planned to put a lot of music files on it I would consider doubling that since those files are much larger than gpx files. As for the 396 with a 64GB card, IDK. My sense is that not much has changed with SD cards in Garmin device for a long time since they still require FAT32 formatting. If you already have a 64 GB card then there is no harm in trying it.

Peobody wrote: Sat Mar 07, 2026 2:08 pm but I know I would have chosen significantly smaller than 65536 if I had the choice.

Maybe I should format a 128gb cards allocation size half that 65536 ?
so allocate the 128 gb card to size 32768 ?
since 4 x 32 = 128 gb
I don't see anything greater than selecting the max 32768 allocation size on this fat32guiformat.exe free download program i downloaded last nite
I think using a 128 gb sd card is probably the maximum size card that can be used in a 396 for fat32 formatting
dunno,
wow I hate math, failed it all thru school since grade 1 lol
my poor Teachers lol

Peobody wrote: Sat Mar 07, 2026 2:08 pm My sense is that not much has changed with SD cards in Garmin device for a long time since they still require FAT32 formatting.

ya from what I was reading, all of the Garmin Zumo's including XT2 and XT3's all require the maximum file size to be 4gb or less, Garmin requires them all to be FAT32 I think

That 4GB file size limit is not a Garmin thing. It is a file size limit of the FAT32 formatting.

Edit: It's a beautiful day in the neighborhood (at least my neighborhood) so I'm suiting up and heading out on a ride.

twowheelstom wrote: Sat Mar 07, 2026 2:30 pm should format a 128gb cards allocation size half that 65536 ?
so allocate the 128 gb card to size 32768 ?
since 4 x 32 = 128 gb
I don't see anything greater than selecting the max 32768 allocation size on this fat32guiformat.exe free download program

i got that wrong, the max allocation size showing on that fat32 format program is 65536

told ya that I failed math lol

ignore all my math, i got it all wrong,

twowheelstom wrote: Sat Mar 07, 2026 3:15 pm i got that wrong, the max allocation size showing on that fat32 format program is 65536

Does it give you choices of smaller sizes?

FWIW, I used the free version of AOMEI Partition Assistant.

Peobody wrote: Sat Mar 07, 2026 9:51 pm

twowheelstom wrote: Sat Mar 07, 2026 3:15 pm i got that wrong, the max allocation size showing on that fat32 format program is 65536

Does it give you choices of smaller sizes?

Yes, cluster allocation size choices are:
guiformat.exe
Allocation Unit Size:
512
1024
2048
4096
8192
16384
32768
65536