---
title: Drive transfers
description: How file transfers work for each kind of drive, and how to limit the ones that pass through your server.
---
When someone downloads or uploads a file in a drive, the bytes take one of two paths.
- **Direct:** the file goes straight between the browser and the provider. Your server does not carry it. Google Drive, OneDrive and S3 servers set to `direct` work this way.
- **Relayed:** the file passes through your server. WebDAV, FTP, FTPS and SFTP drives always work this way, because a browser cannot talk to those servers itself. An S3 server set to `relay` works this way too.
Relayed transfers need the secret `METIS_DRIVE_RELAY_SECRET`, of at least 32 characters, as soon as you list a relayed server. You can generate one with `openssl rand -base64 32`. The bootstrap script generates it. Relayed transfers need an always-on server, not a serverless host.
## Limit relayed transfers
Open **Dashboard**, **System**, **Instance**. The **Drive relay** card has two limits:
| Field | Default | What it limits |
| --- | --- | --- |
| **Max transfer size (MB)** | 256 | The size of each relayed file. |
| **Transfers per user, per process** | 3 | How many relayed transfers one person can run at the same time. |
Change a value, click **Save changes** and enter your authenticator code.
To set the starting values before the first start, use `METIS_DRIVE_RELAY_MAX_MB` and `METIS_DRIVE_RELAY_CONCURRENCY`.
## Limit connections to a server
FTP and SFTP entries have a **Pool size**: the total number of connections Metis Suite opens to that server, shared by all users. The default is 2 for FTP and 3 for SFTP. Keep it under the server's connection limit per IP address. See [Server lists](/self-hosting/configure/server-lists).