Sizing cloud disk for call recordings

Most VICIdial admins underestimate disk when moving to the cloud. The database and OS are small, but a Call recording archive grows steadily with every dialing hour, and the bill for running out of space mid-campaign is higher than the cost of provisioning extra storage upfront.

This post walks through how to calculate the storage you actually need, how Recording format (WAV/MP3) choices affect that number, and how to set a retention policy that keeps costs under control.

How much space does each call actually use

VICIdial stores recordings in /var/spool/asterisk/monitor/ by default. File size depends on the Recording format (WAV/MP3) you configure in the campaign settings. GSM and MP3 are the most common compressed formats and come in around 1 to 4 MB per call-hour of audio. Uncompressed G.711 WAV runs closer to 8 MB per hour for mono audio. Stereo recording, which captures both sides on separate channels, doubles all of those figures.

As a practical baseline: if your center runs 50 Concurrent calls and agents average 45 minutes of talk time per hour, you are generating roughly 37.5 call-hours of audio per hour of operation. At GSM rates that is about 75 to 150 MB per operating hour, or 1.8 to 3.6 GB per 24-hour day.

Disk sizing formula

flowchart TD
  A[Calls per day] --> B[Avg talk minutes per call]
  B --> C[Total call-minutes per day]
  C --> D{Recording format?}
  D -->|GSM / MP3| E[~1-4 MB per call-hour]
  D -->|WAV mono| F[~8 MB per call-hour]
  D -->|Stereo| G[Double the above]
  E --> H[Daily GB estimate]
  F --> H
  G --> H
  H --> I[Multiply by retention days]
  I --> J[Add 30% headroom]
  J --> K[Minimum disk size]

The formula is straightforward. Take your calls per day, multiply by average talk time in minutes, divide by 60 to get call-hours, multiply by your per-hour MB rate, then multiply by how many days of Recording retention you need. Add at least 30 percent headroom for OS, logs, and DB growth. Here is a worked example for a 20-seat center:

# 20 agents, 200 calls/day, avg 8 min talk time, GSM at 2 MB/call-hour, 90-day retention
call_hours_per_day = (200 * 8) / 60  # = 26.7 hours
daily_gb = 26.7 * 2 / 1024           # ~= 0.052 GB
total_gb = 0.052 * 90                 # ~= 4.7 GB raw
disk_needed = 4.7 * 1.30             # ~= 6.1 GB for recordings alone

This example is small, but scale it to a 200-seat floor with 2000 calls per day in WAV format and 180-day retention and you are looking at hundreds of gigabytes. The point is to do the math before you provision, not after you hit df -h and see 95 percent usage.

Format tradeoffs

GSM is the VICIdial default and a reasonable choice for most compliance-driven recordings. It is small and plays back in most media players. MP3 is similar in size and more universally supported but requires a codec license on some Asterisk builds. WAV keeps audio uncompressed, which matters if you are running voice analytics or transcription tools that need full-fidelity audio. Stereo WAV is the largest format by a wide margin and is only worth the storage cost if your quality team genuinely listens to both sides in separate channels.

A common approach is to record in GSM for daily operations and configure a cron job to re-encode important calls to MP3 for longer archival. This keeps the active dataset small while preserving quality for escalations.

Retention policy and disk lifecycle

Recording retention is as much a legal question as a technical one. Many call centers keep recordings for 30 to 90 days for internal QA and extend to one or two years for regulated industries. Whatever the policy, the retention period directly multiplies your disk requirement.

On a cloud VPS, disk can usually be expanded without downtime on most providers. That makes it less catastrophic to underestimate at first, but an expansion still requires planning and a short maintenance window on some setups. Sizing correctly from the start avoids the scramble. For more on protecting recordings across rebuild events, see snapshots and backups for a cloud VICIdial box.

VICIfast and disk management

With Managed hosting on VICIfast, disk sizing is part of the Provisioning conversation. The platform is Single tenant, so your recordings never share a disk with another customer's data. The background context on why the cloud approach fits VICIdial is covered in the VICIdial cloud guide.

If you want a fully managed box where disk expansion, snapshots, and recording storage are handled for you, check the options on the pricing page to see which plan fits your call volume.