--- title: "Scratch Disk" slug: "scratch-disk" updated: 2026-02-25T15:27:13Z published: 2026-02-25T15:27:13Z canonical: "docs.fmad.io/scratch-disk" --- > ## Documentation Index > Fetch the complete documentation index at: https://docs.fmad.io/llms.txt > Use this file to discover all available pages before exploring further. # Scratch Disk Scratch Disks are helpful for keeping temporary or persistent data outside of the FMADIO host capture system. Many times the OS disks are unable to be used due to capacity or location. Typical disk allocation is below. The system is designed entirely for Capture ![](https://cdn.document360.io/b9aab0c4-36d0-4616-9673-30b661455571/Images/Documentation/image(47).png?sv=2026-02-06&spr=https&st=2026-11-06T17%3A14%3A50Z&se=2026-11-06T18%3A14%3A50Z&sr=c&sp=r&sig=FljVCzsVuqcCD1jAJ5iEq07pRbB0vUa1C3%2FjoMitQRQ%3D) Modification of this to allow 3 of the capture drives to allocated as Scratch Disk is shown below ![](https://cdn.document360.io/b9aab0c4-36d0-4616-9673-30b661455571/Images/Documentation/image(48).png?sv=2026-02-06&spr=https&st=2026-11-06T17%3A14%3A50Z&se=2026-11-06T18%3A14%3A50Z&sr=c&sp=r&sig=FljVCzsVuqcCD1jAJ5iEq07pRbB0vUa1C3%2FjoMitQRQ%3D) Scratch Disks can be run as a RAID0 or RAIDx group of drives, allows flexible allocation of the total storage capacity of the system between Capture vs Analytics. ## Creating Scratch Disk The steps to create a scratch disk are fairly straight forward. There are a few uses of a scratch, some of the more common examples are: - LXC container - PCAP local storage - Intermediate processing storage - Many more… **NOTE: Reallocating a disk from the capture array requires formatting / loss of all captured data.** ### Step 1) Assign physical disks Start by editing the disk configuration file `/opt/fmadio/etc/disk.lua` In your preferred editor vi or nano edit the file ```plaintext sudo vi /opt/fmadio/etc/disk.lua ``` Then moving serial numbers from the CacheDisk section to the ScratchDisk section. For example moving a single disk (serial number "22443E9DC54E") from ssd8 -> scr0 **Before:** ```plaintext  CacheDisk =    {        ["22443E9D204F"]        = "ssd0",        ["22223AD5BFC3"]        = "ssd1",        ["22443E9D3AFF"]        = "ssd2",        ["22443E9DC543"]        = "ssd3",        ["22443E9D2076"]        = "ssd4",        ["22443E9D3B41"]        = "ssd5",        ["22443E9D3B65"]        = "ssd6",        ["22443E9D20A4"]        = "ssd7",        ["22443E9DC54E"]        = "ssd8",    }    ,    ParDisk =    {        ["22443E9D2087"]        = "par0",    }    ,    RaidDisk =    {    }    ,    ScratchDisk =    {    }    ,    OSDisk =    {    ["50026B7685513F33"] = "os0",    }    , ``` **After: renaming ssd8 to scr0** ```plaintext    CacheDisk =    {        ["22443E9D204F"]        = "ssd0",        ["22223AD5BFC3"]        = "ssd1",        ["22443E9D3AFF"]        = "ssd2",        ["22443E9DC543"]        = "ssd3",        ["22443E9D2076"]        = "ssd4",        ["22443E9D3B41"]        = "ssd5",        ["22443E9D3B65"]        = "ssd6",        ["22443E9D20A4"]        = "ssd7",    }    ,    ParDisk =    {        ["22443E9D2087"]        = "par0",    }    ,    RaidDisk =    {    }    ,    ScratchDisk =    {        ["22443E9DC54E"]        = "scr0",    }    ,    OSDisk =    {    ["50026B7685513F33"] = "os0",    } ``` Save the file. This can be repeated for as many disks as you require, please keep the numbering sequential e.g. scr0, scr1, scr2, scr3 etc so the system can map it correctly. ### Step 2) Reboot the system Rebooting is required as the system needs to rename the mount points in /opt/fmadio/disk ### Step 3) Create RAID partition After reboot is completed confirm the allocated scratch disks are visible in: `/opt/fmadio/disk/scr*` e.g. in the example below 4 disks are allocated for scratch space: ```plaintext fmadio@fmadio200v4-636aaaa:~$ ls -al /opt/fmadio/disk/scr* lrwxrwxrwx    1 root     root            12 Sep 30 05:42 /opt/fmadio/disk/scr0 -> /dev/nvme1n1 lrwxrwxrwx    1 root     root            12 Sep 30 05:42 /opt/fmadio/disk/scr1 -> /dev/nvme2n1 lrwxrwxrwx    1 root     root            12 Sep 30 05:42 /opt/fmadio/disk/scr2 -> /dev/nvme3n1 lrwxrwxrwx    1 root     root            12 Sep 30 05:42 /opt/fmadio/disk/scr3 -> /dev/nvme4n1 fmadio@fmadio200v4-636aaaa:~$ ``` After confirming disks are named correctly, run the following which will create and format scratch disk automatically: ```plaintext sudo /opt/fmadio/bin/format_scratch.lua ``` Example output of a successful run is shown below: (Note: prior to Firmware 2026Q1 pls use `sudo /opt/fmadio/bin/format_scratch.lua` ) ```plaintext fmadio@fmadio200v4-683:~$ sudo /opt/fmadio/bin/format_scratch.lua --disk fmad fmadlua Oct  7 2024 (/opt/fmadio/bin/fmadiolua /opt/fmadio/bin/format_scratch.lua ) calibrating... 0 : 2749997360           2.7500 cycles/nsec offset:0.003 Mhz Cycles/Sec 2749997360.0000 Std:       0 cycle std(  0.00000000) Target:2.75 Ghz ------------------------------------------- umounting------------------------------------------ Cmd [sudo umount /mnt/store1] umount: /mnt/store1: not mounted. Cmd [sudo mdadm --stop /dev/md1] mdadm: error opening /dev/md1: No such file or directory ------------------------------------------- create RAID0 ------------------------------------------ Scratch[1] Mountpoint: scr0 Total Drives: 1 [ /opt/fmadio/disk/scr0] Cmd [/usr/bin/yes | sudo mdadm --create /dev/md1 --force --level=stripe --raid-devices=1 --chunk=64K  /opt/fmadio/disk/scr0] mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md1 started. sleep...0/5 sleep...1/5 sleep...2/5 sleep...3/5 sleep...4/5    /dev/md1:            Version : 1.2      Creation Time : Tue Oct  8 17:47:08 2024         Raid Level : raid0         Array Size : 3750607168 (3576.86 GiB 3840.62 GB)       Raid Devices : 1      Total Devices : 1        Persistence : Superblock is persistent        Update Time : Tue Oct  8 17:47:08 2024              State : clean     Active Devices : 1    Working Devices : 1     Failed Devices : 0      Spare Devices : 0         Chunk Size : 64K               Name : fmadio200v4-683:1  (local to host fmadio200v4-683)               UUID : d5dde191:f70d2f80:046d1b8a:bd5c0abb             Events : 0        Number   Major   Minor   RaidDevice State           0     259       12        0      active sync   /dev/nvme9n1 ------------------------------------------- create file system ------------------------------------------ Cmd [/usr/bin/yes | sudo mkfs.ext4 /dev/md1 2>&1] mke2fs 1.46.5 (30-Dec-2021) Discarding device blocks: done Creating filesystem with 937651792 4k blocks and 234414080 inodes Filesystem UUID: 9019c1b3-f026-4425-a29e-49466632005e Superblock backups stored on blocks:        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,        4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,        102400000, 214990848, 512000000, 550731776, 644972544 Allocating group tables: done Writing inode tables: done Creating journal (262144 blocks): done Writing superblocks and filesystem accounting information: done Cmd [sudo mount /dev/md1 /mnt/store1 2>&1 ] Cmd [sudo chown fmadio.staff /mnt/store1 2>&1] ------------------------------------------- done ------------------------------------------    Total ScratchSize  : 3.751TB    Scratch Mountpoint : /mnt/store1/    Highly recommend to reboot the system. to confirm scratch disk is automatically mounted on reboot fmadio@fmadio200v4-683:~$ ``` ### Step 4) Reboot the system Its highly recommended to reboot the system. This ensures on reboot the scratch disks are mounted correctly after reboot. ```plaintext sudo reboot ``` ### Step 5) Confirm scratch disk is present The scratch by default gets mounted to: `/mnt/store1/` There should be a logfile named scratch.log which is the log file from Step 3). ### Step 6) Reformat the capture array As the capture array has now lost a disk. Its unable to capture correctly. Go to the TOOLS page on the WWW GUI, and click on the Quick Format menu item. ![](https://cdn.document360.io/b9aab0c4-36d0-4616-9673-30b661455571/Images/Documentation/image(12).png?sv=2026-02-06&spr=https&st=2026-11-06T17%3A14%3A50Z&se=2026-11-06T18%3A14%3A50Z&sr=c&sp=r&sig=FljVCzsVuqcCD1jAJ5iEq07pRbB0vUa1C3%2FjoMitQRQ%3D) This will take approx. 5 minutes. It is only formatting the custom FMADIO Filesystem (not every byte of capture data) thus its fairly fast to run. The system will reboot once, going into “Safe Mode” so the format can be completed without interruption. Then reboot again and back to regular operation. ### Step 7) Finish The scratch disk can now be used as a regular linux file system Scratch Disks are helpful for keeping temporary or persistant data outside of the FMADIO host capture system. Many times the OS disks are unable to be used due to capacity or location.