You really need to give us some more details on the system and os you're going to use. Every os and platform has is own limits and possibilities.

i.e. most 386 and 486 have a limit for 512Mb by default. Most pentiums go up to 8GB, but there you're into the PCI age with other solutions. XT ide bios extensions may overcome this limits.

DOS 3.2 Will go up to 30MB partitions, DOS 6.22 Will go up to 2GB partitions with the limit of 8GB hard disk and dos 7 wil give you fat32 with theoretically 128GB limit. You might look at Linux distro but I'm not into that too give you advice. Also look at software that can use space beyond bios limits.

Having a compact flash card is reliable and brings down stress on old hardware. And it makes it easy to transfer data from and to modern hardware. Newer harddisks (80GB + hard disks) will be more reliable and fill up the ISA bandwidth.

SCSI Will be an option, if you can find a controller and disks. Reliability is so-so because lots of these disks came from servers that were turned on for 24/7 on heavy load and thus are worn out.

So, where you at?

You’re going to need an ISA disk (IDE) controller card at a bare minimum.
There are options for multi-IO cards that have IDE, Floppy, COM and LPT ports and most likely that is what you will find because they were common.

You can use a compact flash adapter with that card below 2GB or an SD to IDE adapter with a small SD card below 2GB, but without the IDE card and without any IDE or floppy controller onboard, you’re stuck.

Larger capacity storage is dependent on what’s supported by your BIOS. Some 486 boards can use 8GB and then there are options to use an old LAN card with bootrom to enable larger disk support, but that’s another topic in itself.

Hey thanks for answers . I have 486 sx with Biostar MB-1440UCV or similar. Primarily im going to use dos 6.22 . Id like to have card that could be usable in 286 so i can test it aswell. Like universal solution. I do have DOM 512mb so i can put it in . Reason i asked that ISA 16 bit has 8 years before PCI and tech advance significally over this time .So if i get IDE card from 1984 it would be worse than from 1992 in suppoerted capacity and speeds . If i can hear brand and model that provides good characteristics thats would be cool.I dont want bothering with scsi and i have seen cards 8 bit ISA CF adaters for 8 bit ISA but i dont think its any good for me.

With DOS 6.xx You're going to have these limits:
+ 2GB partition
+ 8GB total hard disk space
Having an 8GB industrial cf card would be the most convenient solution. You may get a cheap ide to cf adapter from AliExpress, most of them also work flawlessly.

If you have a regular ISA ide controller, you may face the 512MB limit from the bios. If you have a network card with empty flash socket you may get a 28c eeprom and load xt ide universal bios onto it. It'll take over the ide controller in its full 16 bit capability. You don't need those 8b controller cards, those are intended for XT class computers and maybe some earlier 286 (but do work up to pentium 3 class)

Moving to DOS 7 wil add fat32 and xt ide will give you several more GB usable with bigger disks. DOS 7 had is remarks with Windows prior to 9x so that's something to keep in mind.