Topic

Block Device

1 post about Block Device. Every summary links to the original.

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Modal
Building fast filesystems for VMs
Modal’s VM Sandboxes originally used virtio-fs on top of ImageFS, a lazy-loading FUSE filesystem. This stack caused severe performance degradation: recursive chown took over a minute instead of seconds, and tools like bun install and ripgrep ran three times slower. Analysis revealed that every metadata operation like chown required three round trips from the guest VM to the host, each incurring approximately 99 µs overhead. Modal replaced virtio-fs with ImageFS-blk, a block-level solution that presents a virtual block device to the guest, letting the kernel manage its own filesystem. The new approach delivers dramatic speedups: chown dropped from 9.87 to 0.21 seconds, and bun install fell from 12.5 to 1.07 seconds, often exceeding even direct ImageFS performance.

The best engineering reads, once a week.

Topic

1 post about Block Device. Every summary links to the original.

Paid picks we use ourselves. Links carry a referral code — a subscription through one earns us a commission at no extra cost to you.

Newest first

Modal
Building fast filesystems for VMs
Modal’s VM Sandboxes originally used virtio-fs on top of ImageFS, a lazy-loading FUSE filesystem. This stack caused severe performance degradation: recursive chown took over a minute instead of seconds, and tools like bun install and ripgrep ran three times slower. Analysis revealed that every metadata operation like chown required three round trips from the guest VM to the host, each incurring approximately 99 µs overhead. Modal replaced virtio-fs with ImageFS-blk, a block-level solution that presents a virtual block device to the guest, letting the kernel manage its own filesystem. The new approach delivers dramatic speedups: chown dropped from 9.87 to 0.21 seconds, and bun install fell from 12.5 to 1.07 seconds, often exceeding even direct ImageFS performance.

The best engineering reads, once a week.