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VirtuCache caches all VM reads and writes to host NVME at Yeoju University

Use Case:
Storage Performance

Yeoju County, South Korea


  • Customer wanted very low VM latencies for their write intensive Oracle VMs.


  • Virtucache ensured that storage latencies at the VM level were consistently under 2ms for Yeoju University's Oracle based Student Information System.

VirtuCache caches all VM reads and writes to host NVME at Yeoju University

The Virtunet Difference
The customer selected VirtuCache because:
  • VirtuCache was the only solution in the market that improves storage performance without requiring a wholesale replacement of customer's storage infrastructure.
  • The only other alternative was to replace CEPH storage with a faster All-Flash array which would have been very expensive.
  • April 23,2021; Yeoju County, Korea.

    Yeoju University uses VirtuCache with HGST NVME Flash drives to improve Oracle application performance.

    VirtuCache is software from Virtunet Systems that caches VM read and writes to in-host SSD or RAM.

    Yeoju University is a private educational institution in Southern Gyeonggi province in S. Korea.

    Yeoju VMware and Storage Environment.

    Yeoju University is running Student Information System software on Oracle databases. The SIS application is running in 100 odd VMs on a 3-host VMware cluster. The underlying storage was built using CEPH storage software that was running in VMs. CEPH is open source software that clusters together locally attached SSDs / HDDs and presents it to compute nodes (in this case VMware) over iSCSI, NFS, and other shared storage protocols.

    High Storage Latency in CEPH.

    CEPH storage software exhibits high latencies, especially for writes. This is because of high software overhead in CEPH, especially because CEPH replicates all the writes to another node (for data protection). If CEPH is run in VMs, as was the case at Yeoju, you have the additional overhead of VMware’s VMFS filesystem. Even though Yeoju is using SSDs with CEPH, the write latencies were high all the time.

    VirtuCache configuration to reduce latencies in Oracle application VMs.

    VirtuCache automatically caches all data from VMware VMs to in-host SSD or RAM. At Yeoju University, VirtuCache is configured to cache all VMware Datastores (which were on CEPH storage) to a 3.2TB NVME SSD from HGST (model HUSMR7632) per host.

    In VirtuCache, you can apply three caching policies.

      1. Write Through Caching policy that caches reads but not writes.

      2. ‘Write-Back with One Replica’ caching policy that caches reads and writes, and it mirrors (replicates) writes to one additional host in the ESXi cluster. VirtuCache mirrors writes to protect against data loss if the host fails.

      3. ‘Write-Back with No Replica’ works like the ‘Write-Back with One Replica’ caching policy, except that it does not replicate writes to another host, which means that if a host fails then there will be data loss for the VMs that have this policy.

    The customer’s mission critical Oracle application software couldn’t tolerate any data loss, as a result, VirtuCache’s ‘Write-Back with No Replica’ policy was not an option. Also they wanted to primarily accelerate writes from VMs, hence the simpler ‘Write-Through’ caching policy was not an option either. They ended up applying the ‘Write-Back with One Replica’ caching policy to all the Datastores in this 3-host ESXi cluster. So all reads and writes from all the Datastores are cached to the in-host NVME SSD. In the ‘Write-Back with One Replica’ caching policy, VirtuCache also mirrors the write cache to cache media in another host. This is to protect against data loss in case a host fails. For additional details about this policy, review this link.

    Performance Improvement with VirtuCache.

    VM Latency Before VirtuCache.

    VM Latency After VirtuCache.

    VM latency


    Less than 2ms. With VirtuCache caching to in-host HGST 3.2TB NVME SSD.

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