Merge branch 'ssd_doc' into 'master'

Document ephemeral SSD usage

See merge request !24

gui/README.md

@@ -102,3 +102,12 @@ os_distro=ubuntu # example
 ## Add SWAP file to instance
 
 By default VMs after creation do not have SWAP partition. If you need to add a SWAP file to your system you can download and run [script](https://gitlab.ics.muni.cz/cloud/cloud-tools/blob/master/swap.sh) that create SWAP file on your VM.
+
+## Local SSDs
+
+Default MetaCentrum Cloud storage is implemented via CEPH storage cluster deployed on top of HDDs. This configuration should be sufficient for most cases.
+For instances, that requires high throughput and IOPS, it is possible to utilize hypervizor local SSDs. Requirements for instances on hypervizor local SSD:
+* instances can be deployed only via API (CLI, Ansible, Terraform ...), instances deployed via web gui (Horizon) will always use CEPH for it's storage
+* supported only by flavors with ssd-ephem suffix (e.g. hpc.4core-16ram-ssd-ephem)
+* instances can be rebooted without prior notice or you can be required to delete them
+* you can request them, when asking for new project, or for existing project on cloud@metacentrum.cz