In early medieval Ireland, slavery and the slave trade actually increased dramatically starting around the mid-9th century thanks to the establishment of permanent Scandinavian settlements and their associated markets on the island. Scandinavian raiders based in these settlements took to enslaving indigenous Irish people, as well as Picts, Britons and English people from across the Irish Sea. As well, indigenous Irish lords saw this as an opportunity to gain influence, power and money by willingly taking part in the slave trade; captives from endemic warfare would be sold to these centers of trade. Dublin during this period was actually home to the largest slave market in western Europe. As in other agrarian societies, many individuals in Ireland fell into slavery by way of debt.

Slavery in medieval Ireland was very different from what you'd see in the American south. Slaves were recognized to have some basic legal rights, including rights to property, although slave owners were allowed to inflict corporal punishment on disobedient slaves. Male slaves would have been engaged in pastoral or agrarian labour, possibly watching herds and shepherding, which Saint Patrick was put to as a slave in pre-Christian Ireland. Female slaves appear to have been employed in domestic labour; annalistic evidence makes reference to women being carried off and enslaved to grind oats into flour for their captors. Female slaves called cumals were actually the highest unit of value in the Irish economic system, although by the historical period this may have been simplified into an abstract value worth however much cattle or ounces of silver.

If you'd like to know more I can checkout my notes on Fergus Kelly's Guide to Early Irish Law when I get home.

Edit: Legal evidence indicates that it was seen as taboo to free a slave (with some exceptions; an early Penitential urges men who impregnate their female slaves to set them free) with the implication that slave owning was a basic element of a wealthy individual's prosperity. It was seen as a morally irresponsible and socially devious act that could bring about supernatural retribution in the form of crop failure, droughts, livestock diseases etc. I wrote above that slaves enjoyed some legal rights which may be misleading. Slaves only had rights in the context of their role as another person's property: slaves could only make contracts under their master's orders for example. They could not serve as witnesses during trials, and were unprotected by the law if assaulted or killed by their master.