list "(USB) Floppy Diskette Drive" as one of the hardware requirements.
As for storage, the Z820, at least, includes an XP-compatible LSI 6Gbps SAS controller onboard in addition to SATA, so performance with SAS and/or SATA drives shouldn't be an issue.
High core count, dual-socket Z820s are readily available on the used market for <$1,000, and seem like they'd make excellent high-end XP boxes (and even better Windows 10/Linux boxes; I'm running both under ESXi with GPU passthrough on mine; licensing issues aside, current [10.14 and 10.15] OS X versions also work, including GPU passthrough, at least in the case of the NVIDIA Quadro K2000 and Apple-supplied drivers).
More generally, XP-compatible 6Gbps SAS PCIe RAID cards and HBAs are readily available on eBay for peanuts, so that'd probably be the way to go if you want the best disk performance under XP with (relatively) modern hardware.
Evidence: HP's instructions for installing Windows XP from retail media on (ca. 2012) Zx20 workstations
http://h10032.www1.hp.com/ctg/Manual/c03366531
list "(USB) Floppy Diskette Drive" as one of the hardware requirements.
As for storage, the Z820, at least, includes an XP-compatible LSI 6Gbps SAS controller onboard in addition to SATA, so performance with SAS and/or SATA drives shouldn't be an issue.
High core count, dual-socket Z820s are readily available on the used market for <$1,000, and seem like they'd make excellent high-end XP boxes (and even better Windows 10/Linux boxes; I'm running both under ESXi with GPU passthrough on mine; licensing issues aside, current [10.14 and 10.15] OS X versions also work, including GPU passthrough, at least in the case of the NVIDIA Quadro K2000 and Apple-supplied drivers).
More generally, XP-compatible 6Gbps SAS PCIe RAID cards and HBAs are readily available on eBay for peanuts, so that'd probably be the way to go if you want the best disk performance under XP with (relatively) modern hardware.