Network Storage
Sharing storage between hosts, over files (NFS, Samba) and over blocks (iSCSI, NBD). NFS is the core skill for RHCSA and LFCS, and a hung NFS mount is a frequent production incident.
Revision Card
| Fact | Value |
| NFS exports | Files; many clients share one filesystem |
| iSCSI exports | Blocks; one host owns the raw disk |
| Exports file | /etc/exports, applied with exportfs -rav |
| NFS version | NFSv4.2 over TCP, single port 2049 |
| hard vs soft | hard blocks forever (safe); soft fails (risks corruption) |
| Hang signature | D state, WCHAN rpc_wait_bit_killable, load up, CPU idle |
| root_squash | Client root maps to nobody on the export |
| Autofs | Mounts on access, unmounts when idle |
| Samba/CIFS | SMB protocol; mount -t cifs with a credentials file |
| iSCSI ports | TCP 3260; target with targetcli, initiator with iscsiadm |
| Task | Command |
| Export a directory | edit /etc/exports; sudo exportfs -rav |
| Show server exports | exportfs -s; showmount -e SERVER |
| Mount NFS | mount -t nfs SERVER:/path /mnt |
| Find a hung NFS process | ps -eo stat,wchan,comm | grep '^D' |
| Autofs on demand | master map + map file; systemctl restart autofs |
| Mount CIFS safely | mount -t cifs //srv/share /mnt -o credentials=FILE |
| iSCSI discover/login | iscsiadm -m discovery; iscsiadm -m node --login |
| New iSCSI disk | lsblk -S |
Topic Map
| File | Covers | Track | Weight |
| NFS | Exports, mounts, hard vs soft, the D-state hang, root_squash | Core | Med |
| Autofs | Master and map files, on-demand mount, idle timeout | RHCSA | Low |
| Samba and CIFS | Serving SMB, client mount with a credentials file | RHCSA | Low |
| iSCSI and NBD | Block export, target and initiator, IQN, ACL, NBD | Advanced | Low |
Scenarios and Labs