What is vajra hell

/gzhan yang 'jam  dpal sgyu dra ba'i rgyud las/  

dbang bskur sogs thob slob dpon la/ / rmongs par gyur pa'i slob ma yis/ 

/sbyor ba'i dngos gzhi rab rdzogs pas/ / rtsa ba yan lag nyams gyur na/ 

/blo ngan slob mas bshags par bya/ /gal te ma bshags dus 'das na/ 

/phyi yi rgya mtsho chen po yi/ /chu de skra yis gter nus pa/ 

/de yi tshad du sdug bsngal myong/ /rdo rje dmyal bar grags pa yin/

Furthermore, in the Mañjuśrījñālamahātantra, it is said:

If a disciple who has become deluded, despite having received the initiations and having fully completed the preparatory and main practices from a Vajra Master, transgresses the root and branch samayas, the foolish disciple must confess them. If one does not confess them and the time passes, one will experience suffering to the extent of being able to remove the water of the great outer ocean with a single hair; this is what is known as the Vajra Hell.

D2488 - rdo rje theg pa'i rtsa ba'i ltung ba'i rgya cher bshad pa - from 69--105pgs - Mañjuṣrīkīrti ('jam dpal grags pas)

AT1391 - IA - non-final - A3405 - 771-772