Move a terabyte — a chain reaction

Bits, bytes and the factor of eight

Links are sold in bits per second and files are measured in bytes. That factor of eight is where most bad estimates come from, before overheads have even been considered.

15 GB at 100 Mbps≈22 min

Factor8 bits per byte

Real-world efficiency≈90%

Rule of thumbDivide the megabits by eight to get megabytes, then take about 10% off for protocol overhead. Anything better is a pleasant surprise.

Open Data Transfer Time with these numbers →

Now scale it to the real job

Change the size to a terabyte and the same link stops being an afternoon. This is the moment people discover that posting a disk is genuinely faster — a calculation worth doing before committing to the copy.

1 TB at 100 Mbpsabout a day

Sneakernetoften faster

Rule of thumbNever underestimate the bandwidth of a parcel. Latency is terrible, but throughput is enormous.

Open Data Transfer Time with these numbers →

Work out what the array actually gives you

RAID levels trade capacity, speed and redundancy against each other. The tool shows usable capacity and how many drives you can lose — which is rarely the number people assume.

RAID 5one drive of parity

RAID 6two

RAID 0none — and doubles your risk

Rule of thumbRAID is not a backup. It protects against a drive dying, not against deleting the wrong folder.

Open RAID Calculator →

Make sure the network can even reach it

A fast link into the wrong subnet is no link at all. Subnetting decides how many hosts fit and which machines can see each other — worth confirming before blaming the cable.

/24254 usable hosts

/302 — a point-to-point link

Rule of thumbEvery subnet loses two addresses: the network and the broadcast. A /31 is a special case for links, not a general rule.

Open Subnet Calculator →

Bits, bytes and the factor of eight

Now scale it to the real job

Work out what the array actually gives you

Make sure the network can even reach it

Do the division before the copy