cktDesigner
Cadet
- Joined
- Aug 30, 2017
- Messages
- 5
I'm building my first FreeNAS system and am pondering what type of device to use for an SLOG device. The main intent for the system is file storage, but I will probably run one or two VMs as well, and the reading I have done indicates that having an SSD for the SLOG device should improve performance.
Section 28 (ZFS Primer) of the User Guide (11.0-U2) states that "ZFS currently uses 16 GB of space for SLOG", and that larger ones would be a waste.
The discussion "Some insights into SLOG/ZIL with ZFS on FreeNAS" suggests the fastest device (you can afford), both in actual speed, and minimal latency. The "best" suggestion is for a card that contains Flash memory on a PCI 3.0 card (and is probably the most expensive one). The FreeNAS Hardware guide suggest the Intel P3700 series. While this has great performance, it is very expensive (and the capacity far exceeds the 16 GB that the User Guide indicates is the max the system will use... I hate to spend a lot, then not really use the majority of the capacity.)
Other suggestions, read from various places, suggest that the SLOG be mirrored, and that each pool should have its own (separate device).
So some possibilites, (read/write times in Mbps):
1. Intel P3700. Great performance, but very expensive, plugs into motherboard expansion slot. Has read/write of 2800/2000.
2. Small, fast SSDs (but connected directly to the motherboard, not via an HBA for latency reasons). A small, inexpensive one will have read/write of 500/320.
3. SuperDOMs (SuperMicro boards support these). They are relatively small and have read/write times of 500/145 (and still use SATA).
4. M.2 card (My SuperMicro board supports one of these). One that is reasonably prices has a read/write time of 1850/570.
5. Add a PCI expansion card (like: SEDNA - PCIe 4X - Quad mSATA SSD RAID Controller Card ( RAID 0/1/10) Marvell HyperDuo Technology - Newegg.com) that holds 4 mSATA SSD cards. One mSATA card I looked at had read/write of 550/510.
6. Add a PCI expansion card (like: 2-Slot M.2 SSD Controller Card - PCI Express | StarTech.com) that holds 2 M.2 cards and plugs into a PCIe 4x slot. Saves the SATA connectors for HDDs (vs a regular SSD) and is faster than a regular SSD.
Questions:
1. Given the speed of M.2 (versus regular SSD/SATA), could the motherboard M.2 be partitioned, using one section for SLOG (~16 GB) and the rest for something else (ZIL?)?
2. Has anyone used the PCI expansion method (5 or 6 above for mSATA or M.2 respectively) for SLOG and/or boot? Using a single PCI slot to hold 4 mSATA (2 for mirrored boot and 2 for mirrored SLOG) sounds interesting, but does freeNAS support this? Am I overlooking something that is wrong with a setup like this?
If freeNAS supports it, I was thinking of using suggestion 5 (above) to hold 2 mirrored boot mSATA cards and 2 mirrored SLOG cards, then using the M.2 motherboard socket for a ZIL M.2 SSD. This would free up all the SATA connectors for HDD storage. Or use suggestion 6 for M.2 cards for the SLOG (since M.2 is faster than mSATA).
Comments? Thoughts? Suggestions?
Thanks!
Section 28 (ZFS Primer) of the User Guide (11.0-U2) states that "ZFS currently uses 16 GB of space for SLOG", and that larger ones would be a waste.
The discussion "Some insights into SLOG/ZIL with ZFS on FreeNAS" suggests the fastest device (you can afford), both in actual speed, and minimal latency. The "best" suggestion is for a card that contains Flash memory on a PCI 3.0 card (and is probably the most expensive one). The FreeNAS Hardware guide suggest the Intel P3700 series. While this has great performance, it is very expensive (and the capacity far exceeds the 16 GB that the User Guide indicates is the max the system will use... I hate to spend a lot, then not really use the majority of the capacity.)
Other suggestions, read from various places, suggest that the SLOG be mirrored, and that each pool should have its own (separate device).
So some possibilites, (read/write times in Mbps):
1. Intel P3700. Great performance, but very expensive, plugs into motherboard expansion slot. Has read/write of 2800/2000.
2. Small, fast SSDs (but connected directly to the motherboard, not via an HBA for latency reasons). A small, inexpensive one will have read/write of 500/320.
3. SuperDOMs (SuperMicro boards support these). They are relatively small and have read/write times of 500/145 (and still use SATA).
4. M.2 card (My SuperMicro board supports one of these). One that is reasonably prices has a read/write time of 1850/570.
5. Add a PCI expansion card (like: SEDNA - PCIe 4X - Quad mSATA SSD RAID Controller Card ( RAID 0/1/10) Marvell HyperDuo Technology - Newegg.com) that holds 4 mSATA SSD cards. One mSATA card I looked at had read/write of 550/510.
6. Add a PCI expansion card (like: 2-Slot M.2 SSD Controller Card - PCI Express | StarTech.com) that holds 2 M.2 cards and plugs into a PCIe 4x slot. Saves the SATA connectors for HDDs (vs a regular SSD) and is faster than a regular SSD.
Questions:
1. Given the speed of M.2 (versus regular SSD/SATA), could the motherboard M.2 be partitioned, using one section for SLOG (~16 GB) and the rest for something else (ZIL?)?
2. Has anyone used the PCI expansion method (5 or 6 above for mSATA or M.2 respectively) for SLOG and/or boot? Using a single PCI slot to hold 4 mSATA (2 for mirrored boot and 2 for mirrored SLOG) sounds interesting, but does freeNAS support this? Am I overlooking something that is wrong with a setup like this?
If freeNAS supports it, I was thinking of using suggestion 5 (above) to hold 2 mirrored boot mSATA cards and 2 mirrored SLOG cards, then using the M.2 motherboard socket for a ZIL M.2 SSD. This would free up all the SATA connectors for HDD storage. Or use suggestion 6 for M.2 cards for the SLOG (since M.2 is faster than mSATA).
Comments? Thoughts? Suggestions?
Thanks!