> ## Documentation Index
> Fetch the complete documentation index at: https://docs.archil.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Metering

> How Archil measures active data in the high-speed storage layer

Archil disks use a high-speed, durable cache to enhance performance when working with data from
[data sources](/concepts/data-sources). You are only charged for data actively stored in this
cache layer. For pricing details, see [Pricing & Billing](/administration/billing).

## File data

When reading data from a data source, Archil automatically caches it in the high-speed storage
layer. Cached data remains active for up to 1 hour after your last access.

Writes are buffered in the high-speed storage layer for coalescing before being flushed to the
data source. Recently written data remains active for up to 1 hour after it has been flushed.

The amount of active data may not exactly match the amount you've read or written. Archil
prefetches and caches data ahead of sequential reads, which can result in additional cached data.
Rapid overwrites to the same file will also result in additional active data while Archil
asynchronously coalesces and flushes the writes.

## File metadata

Metadata accesses (e.g., `find`, `ls`, `stat`) do not cause file data to become active and incur
no metering charges.

Metadata writes (e.g., rename, `chmod`) are counted as 32 KiB of active data per operation until
the change is propagated to the data source.

Taking ownership of a path with [`archil checkout`](/reference/archil-cli#checkout) lets Archil
coalesce the many small attribute updates a workload produces into larger chunks before metering
them. For example, `git clone`-ing a 15 MB repository into a checked-out directory is metered as
roughly fifteen 1 MiB writes rather than the thousands of individual metadata operations the client
issues.

## How billing is calculated

Archil meters the amount of active data each minute. Your monthly bill is the time-weighted
average of active data over the billing period, charged at \$0.20 per GiB-month.

For example, if you store 100 GiB for half of a month, you are billed for 50 GiB-months.

You can monitor your active data usage in the [Archil console](https://console.archil.com) on
each disk's **Usage** tab, or on the [Billing](https://console.archil.com/billing) page for an
account-wide view.

## Branches and checkpoints

[Branches and checkpoints](/concepts/branches-and-checkpoints) are copy-on-write. Forking a branch
or taking a checkpoint does not duplicate the underlying data — you are billed once for the shared
base data, plus only the unique data each branch or checkpoint adds.

For example, a 100 GiB parent disk with 50 branches that each modify \~5 GiB of unique data is
metered as roughly **350 GiB total** — the shared 100 GiB base plus the \~250 GiB of unique
per-branch changes — not as 51 full copies (\~5,100 GiB). A checkpoint retains its unique data for
as long as it exists; deleting a checkpoint removes that data from your bill.