50 lines
2.4 KiB
Markdown
50 lines
2.4 KiB
Markdown
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[Documentation](../../README.md#documentation) → Performance → Vitastor's Theoretical Maximum Performance
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-----
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[Читать на русском](theoretical.ru.md)
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# Vitastor's Theoretical Maximum Performance
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Replicated setups:
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- Single-threaded (T1Q1) read latency: 1 network roundtrip + 1 disk read.
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- Single-threaded write+fsync latency:
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- With immediate commit: 2 network roundtrips + 1 disk write.
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- With lazy commit: 4 network roundtrips + 1 disk write + 1 disk flush.
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- Saturated parallel read iops: min(network bandwidth, sum(disk read iops)).
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- Saturated parallel write iops: min(network bandwidth, sum(disk write iops / number of replicas / write amplification)).
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EC/XOR setups:
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- Single-threaded (T1Q1) read latency: 1.5 network roundtrips + 1 disk read.
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- Single-threaded write+fsync latency:
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- With immediate commit: 3.5 network roundtrips + 1 disk read + 2 disk writes.
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- With lazy commit: 5.5 network roundtrips + 1 disk read + 2 disk writes + 2 disk fsyncs.
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- 0.5 in actually (k-1)/k which means that an additional roundtrip doesn't happen when
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the read sub-operation can be served locally.
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- Saturated parallel read iops: min(network bandwidth, sum(disk read iops)).
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- Saturated parallel write iops: min(network bandwidth, sum(disk write iops * number of data drives / (number of data + parity drives) / write amplification)).
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In fact, you should put disk write iops under the condition of ~10% reads / ~90% writes in this formula.
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Write amplification for 4 KB blocks is usually 3-5 in Vitastor:
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1. Journal block write
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2. Journal data write
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3. Metadata block write
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4. Another journal block write for EC/XOR setups
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5. Data block write
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If you manage to get an SSD which handles 512 byte blocks well (Optane?) you may
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lower 1, 3 and 4 to 512 bytes (1/8 of data size) and get WA as low as 2.375.
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Lazy fsync also reduces WA for parallel workloads because journal blocks are only
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written when they fill up or fsync is requested.
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## In Practice
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In practice, using tests from [Understanding Performance](understanding.en.md)
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and good server-grade SSD/NVMe drives, you should head for:
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- At least 5000 T1Q1 replicated read and write iops (maximum 0.2ms latency)
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- At least ~80k parallel read iops or ~30k write iops per 1 core (1 OSD)
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- Disk-speed or wire-speed linear reads and writes, whichever is the bottleneck in your case
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Lower results may mean that you have bad drives, bad network or some kind of misconfiguration.
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