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Using SSD Drives

Parallels Cloud Storage supports SSD drives formatted to the ext4 filesystem and optionally mounted with TRIM support enabled.

Note: Parallels Cloud Storage SSD usage scenario does not generate TRIM commands. Also, modern drives like Intel SSD DC S3700 do not need TRIM at all.

Along with using SSD drives for storing data chunks, Parallels Cloud Storage also supports the use of such drives for special purposes:

  • write journaling . You can attach an SSD drive to a chunk server and configure the drive to store a write journal. By doing so, you can boost the performance of write operations in the cluster by up to 2 and more times.
  • data caching . You can attach an SSD drive to a client and configure the drive to store a local cache of frequently accessed data. By having a local cache on a client's SSD drive, you can increase the overall cluster performance by up to 10 and more times.

Solid-state drive space should be split between write journals and read cache based on the nature of workload, i.e. the proportion of write operations to read operations. The read cache size also depends on how demanding your applications are. If you are unsure, split SSD space in equal parts. For example, if you have a 100GB SSD and four chunk servers on four 1TB HDDs, divide the SSD space as follows:

  • 20 GB reserved for checksums and emergency needs and also to prevent the SSD from filling up completely (because its performance would then degrade),
  • 40 GB for read cache,
  • 40 GB for write journals, i.e. 10 GB per HDD/chunk server.

Checksums require 4 bytes of space for each 4KB page (1:1000 ratio). For example, 4 TB of storage will require 4 GB of space for checksums.

The table below will help you understand how many SSDs you will need for your cluster.

SSD Type

Number of SSDs

Intel SSD 320 Series, Intel SSD 710 Series, Kingston SSDNow E enterprise series, or other SATA 3Gbps SSD models providing 150-200MB/s of sequential write of random data.

1 SSD per up to 3 HDDs

Intel SSD DC S3700 Series, Samsung SM1625 enterprise series, or other SATA 6Gbps SSD models providing at least 300MB/sec of sequential write of random data.

1 SSD per up to 5-6 HDDs

The following sections provide detailed information on configuring SSD drives for write journaling and data caching.

Notes:

1. Not all solid-state drives obey flush semantics and commit data in accordance with the protocol. This may result in arbitrary data loss or corruption in case of a power failure. Always check your SSDs with the pstorage-hwflush-check tool (for more information, see Checking Data Flushing ).

2. We recommend using Intel SSD DC S3700 drives. However, you can also use Samsung SM1625, Intel SSD 710, Kingston SSDNow E or any other SSD drive with support for data protection on power loss. Some of the names of this technology are: Enhanced Power Loss Data Protection (Intel), Cache Power Protection (Samsung), Power-Failure Support (Kingston), Complete Power Fail Protection (OCZ). For more information, see SSD Drives Ignore Disk Flushes .

3. The minimal recommended SSD size is 30 GB.

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