My node is now fully synced in 6 hours. I used parity to sync the node with --geth option. No SSD was needed, working well in RAID:
nohup parity --mode active --tracing off --pruning fast
--db-compaction ssd --cache-size 3072 --geth &
Explanation : Set the operating mode. MODE can be one of: last - Uses the
last-used mode, active if none; active - Parity
continuously syncs the chain; passive - Parity syncs
initially, then sleeps and wakes regularly to resync; dark
- Parity syncs only when the RPC is active; offline -
Parity doesn't sync. (default: last)
Explanation: Indicates if full transaction tracing should be enabled.
Works only if client had been fully synced with tracing
enabled. BOOL may be one of auto, on, off. auto uses last
used value of this option (off if it does not exist).
Explanation: Configure pruning of the state/storage trie. METHOD may be
one of auto, archive, fast: archive - keep all state trie
data. No pruning. fast - maintain journal overlay. Fast but
50MB used. auto - use the method most recently synced or
default to fast if none synced. (default: auto)
Explanation: Database compaction type. TYPE may be one of: ssd -
suitable for SSDs and fast HDDs; hdd - suitable for slow
HDDs; auto - determine automatically. (default: auto)
Note: Server has HDD RAID disk which is quite close to SSD in writes but much much slower (100x slower) in reads. So I think I fooled parity in believing it is on SSD, don't try it on HDD (not sure what will happen )
Explanation: Override database cache size. (default: 128)
Note: I have huge server so I can afford to use 3GB cache. Although cache size seems to boost sync exponentially , be careful with the number.
Explanation: Run in Geth-compatibility mode. Sets the IPC path to be the
same as Geth's. Overrides the --ipc-path and --ipcpath
options. Alters RPCs to reflect Geth bugs. Includes the
personal_ RPC by default.
Note: geth mode is available on parity, later I used geth attach and ran eth functions.
Explanation: Does nothing; warp sync is enabled by default.
Note: Warp is default for Parity , it is amazing feature which syncs Ethereum states fast.
Final note: I don't understand why people are still using Geth, Parity synced entire blockchain in 6-8 hours while Geth could never achieve it (Node was running for weeks). Maybe I was missing something, thoughts are welcome.