Record Time SXT vs MINI Data Rate Calculator odd results

Tue Oct 02, 2018 8:23 pm

I was figuring out how much media to order for a job with a Mini and an SXT and I noticed a strange thing. The record time on a XR Capture Drive (512GB) and a 256GB CFast card were just about the same, even though the CFast card has half the capacity. Sensor settings are the same and the data rates reported are pretty much the same. It seems the Mini can record the same data in half the media space. How is this magic possible?

Here are the links to the Format and Data Rate Calculator results:

SXThttp://www.arri.com/fileadmin/adapps/afdc/AFDC.html?camera=alexaSXT&codec=prores4444xq&resolution=2.39_2K_Ana_SXT&project_rate=23.976p&sensorspeed=96.000&media=XR%20Capture%20Drive%20(512GB)&audio=false

MINIhttp://www.arri.com/fileadmin/adapps/afdc/AFDC.html?camera=mini&codec=prores4444xq&resolution=2.39_2K_Ana&project_rate=23.976p&sensorspeed=96.000&media=CFast%202.0%20256GB%20LEXAR&audio=false
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Jim Denault ASC
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Re: Record Time SXT vs MINI Data Rate Calculator odd results

Wed Oct 03, 2018 4:47 am

Hi Jim,

Sadly there is no magic involved. Quite a ways into the user manual for the SXT you can find this section on internal recording that explains the seeming discrepancy you have encountered:

ProRes RAID - Redundant Recording on XR and SXR Capture Drives
In ALEXA SXT cameras, ProRes is always recorded with a method (RAID) that provides redundancy for greater data security for both XR and SXR Capture Drives. As with ALEXA XT cameras, half the Capture Drive's capacity can be used to record ProRes, but with the SXT, the other half can be used to increase the safety of the recorded data.
ProRes RAID for XR Capture Drives
When XR Capture Drives are being formatted for ProRes in the ALEXA SXT, they
are being formatted as a RAID 1 (mirrored) volume. XR Capture Drives contain two internal SSD drives, and with RAID 1 the same ProRes data is written to each of those two drives.
ProRes RAID for SXR Capture Drives
When SXR Capture Drives are being formatted for ProRes in the ALEXA SXT, essentially the same happens, but since SXR Capture Drives contain four internal SSDs, a combination of RAID 1 (mirroring) and RAID 0 (striping) is used, commonly referred to as RAID 10. Drives zero and one will be combined into one RAID 1 volume and drives two and three into another. This provides redundancy. The resulting two RAID 1 volumes are combined into one RAID 0 volume so it can be accessed as one volume.
Silvan Liu
Service ARRI East Asia Pacific
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