Hello julianuribe

To change a fail disk in your Dell PowerEdge 2900 depends on the RAID controller you have and if you HDD is hotplug or not.

If you have a Hotplug SCSI disk and a PERC controller you need a new disk with the same or more capacity that the disk in the RAID. To change it is very simply, you retire your failed disk and you insert the new one, normally the rebuilding starts automatically.

NOTE: REMEMBER TO HAVE A COMPLETE BACKUP OF YOUR SYSTEM EVERY TIME YOU MANIPULATE DISKS,

If you have other configuration of disks / Raid controller let me know.

Here you have some documentation that can be useful for you:

How to Troubleshoot Hard Drive and RAID Controller Errors on Dell PowerEdge 2900 Servers

Controlador RAID expandible PowerEdge 4/im de Dell

ftp://ftp.dell.com/Manuals/all-products/esuprt_ser_stor_net/esuprt_dell_adapters/dell-perc-4-im_User's%20Guide_es-mx.pdf

Dell PowerEdge Expandable RAID Controller 5/i y 5/E Guía de Usuario

ftp://ftp.dell.com/Manuals/all-products/esuprt_ser_stor_net/esuprt_dell_adapters/poweredge-rc-5i_User's%20Guide_es-mx.pdf

Dell PERC 6/i, PERC 6/E y CERC 6/i Guía del usuario

ftp://ftp.dell.com/Manuals/all-products/esuprt_ser_stor_net/esuprt_dell_adapters/poweredge-rc-6i_User's%20Guide_es-mx.pdf

I hope this information will help you.

Regards,