--- title: Designing for Ephemeral Storage: Why Kubernetes Uses... description: Kubernetes documentation references disk-based merge sort as a primary use case for emptyDir volumes. This post explains why: when sorting data larger than... canonical: https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Designing for Ephemeral Storage: Why Kubernetes Uses Disk-Based Merge Sort to Explain emptyDir | daily.dev og:description: Kubernetes documentation references disk-based merge sort as a primary use case for emptyDir volumes. This post explains why: when sorting data larger than... og:url: https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko og:image: https://api.daily.dev/og/posts/kOHQAAOkO.png og:image:alt: Designing for Ephemeral Storage: Why Kubernetes Uses Disk-Based Merge Sort to Explain emptyDir og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Designing for Ephemeral Storage: Why Kubernetes Uses Disk-Based Merge Sort to Explain emptyDir **[Medium](https://daily.dev/sources/medium_js)** · 4 min read · 1 upvotes · 0 comments ## Summary Kubernetes documentation references disk-based merge sort as a primary use case for emptyDir volumes. This post explains why: when sorting data larger than available RAM (e.g., 100 GB with only 8 GB RAM), an external merge sort algorithm breaks the data into sorted chunks written to local disk, then merges them using small RAM buffers. emptyDir is ideal for this because it uses fast local NVMe storage, avoids costly persistent volume allocations, and is automatically cleaned up when the Pod terminates — making it a perfect scratch space for high-I/O temporary workloads. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How does external merge sort work when a file is too large to fit in RAM? External merge sort splits the large file into smaller chunks that fit in RAM, sorts each chunk in memory, and writes each sorted chunk back to disk as a temporary 'run'. For example, a 100 GB file with an 8 GB RAM limit could be split into 25 sorted 4 GB run files, then merged by reading small slivers from each run and repeatedly picking the smallest value into a final output file. _daily.dev surfaces algorithm deep dives like this for engineers designing memory-constrained data pipelines._ ### Why does the Kubernetes documentation mention disk-based merge sort as a use case for emptyDir volumes? Disk-based merge sort needs somewhere to write large numbers of temporary sorted 'run' files that only matter for the lifetime of the job. An emptyDir volume backs storage directly on the node's disk (such as local NVMe), giving fast I/O for the sort's read/write loops, avoiding the cost of persistent volumes for throwaway data, and getting automatically wiped when the pod is deleted. _Developers designing Kubernetes storage strategies can find similar architecture rationale on daily.dev._ ## Similar posts on daily.dev - [Your Pod Died of “Out of Ephemeral Storage” but the Disk Is Half Empty\!\!](https://daily.dev/posts/your-pod-died-of-out-of-ephemeral-storage-but-the-disk-is-half-empty--jvrjsmjmg) · ITNEXT · 9 upvotes · 1 comments - [k8s-1m Overview](https://daily.dev/posts/k8s-1m-overview-uj6kbjdzt) · Lobsters · 0 upvotes · 0 comments - [Scaling Kubernetes Workloads with Node Swap](https://daily.dev/posts/scaling-kubernetes-workloads-with-node-swap-f7uorbqhg) · Kubernetes · 2 upvotes · 1 comments - [Kubelet watches inodes. Just not until it’s an emergency.](https://daily.dev/posts/kubelet-watches-inodes-just-not-until-it-s-an-emergency--zsh9rqokg) · CNCF · 2 upvotes · 0 comments --- Tags: [#kubernetes](https://daily.dev/tags/kubernetes) [View this post on daily.dev](https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Designing for Ephemeral Storage: Why Kubernetes Uses Disk-Based Merge Sort to Explain emptyDir","url":"https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko"},"datePublished":"2026-07-20T07:33:31.557Z","dateModified":"2026-09-14T08:45:06.890Z","description":"Kubernetes documentation references disk-based merge sort as a primary use case for emptyDir volumes. This post explains why: when sorting data larger than...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/d6ab0a9a223ee01bc82d647f54feb2d2?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/d6ab0a9a223ee01bc82d647f54feb2d2?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Medium","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"kubernetes","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"Designing for Ephemeral Storage: Why Kubernetes Uses Disk-Based Merge Sort to Explain emptyDir"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/designing-for-ephemeral-storage-why-kubernetes-uses-disk-based-merge-sort-to-explain-emptydir-kohqaaoko#faq","mainEntity":[{"@type":"Question","name":"How does external merge sort work when a file is too large to fit in RAM?","acceptedAnswer":{"@type":"Answer","text":"External merge sort splits the large file into smaller chunks that fit in RAM, sorts each chunk in memory, and writes each sorted chunk back to disk as a temporary 'run'. For example, a 100 GB file with an 8 GB RAM limit could be split into 25 sorted 4 GB run files, then merged by reading small slivers from each run and repeatedly picking the smallest value into a final output file. daily.dev surfaces algorithm deep dives like this for engineers designing memory-constrained data pipelines."}},{"@type":"Question","name":"Why does the Kubernetes documentation mention disk-based merge sort as a use case for emptyDir volumes?","acceptedAnswer":{"@type":"Answer","text":"Disk-based merge sort needs somewhere to write large numbers of temporary sorted 'run' files that only matter for the lifetime of the job. An emptyDir volume backs storage directly on the node's disk (such as local NVMe), giving fast I/O for the sort's read/write loops, avoiding the cost of persistent volumes for throwaway data, and getting automatically wiped when the pod is deleted. Developers designing Kubernetes storage strategies can find similar architecture rationale on daily.dev."}}]} ```