7 ms·
Not sure where that belief comes from. But it might be that many benchmarks are naive and compare it against other filesystems in single-disc setups with zero
by rleigh 7y ago
Not sure where that belief comes from. But it might be that many benchmarks are naive and compare it against other filesystems in single-disc setups with zero tuning. Since its metadata overheads are higher, it's definitely slower in this scenario. However, put a pool onto an array of discs and tune it a little, and the performance scales up and up leaving all Linux-native filesystems, and LVM/dm/mdraid, well behind. It's a shame that Linux has nothing compelling to do better than this.
- Jonnax 7y agoHave you seen any benchmarks for the scenario you've described?
- voltagex_ 7y agoHave you got any info on how to do the required tuning that's geared towards a home NAS?
- HorstG 7y agoGroup your disks in bunches of 4 or 5 per Raidz, no more. And have them on the same controller or SAS-expander per bunch. Use striping over the bunches. Don't use hotspares, for performance maybe avoid RAIDz6. Try out and benchmark a lot. Get more RAM, lots more RAM.
- timc3 7y agoBack when I setup my last ZFS running on OmniOS 5 disks was not optimal, though i am running RAIDZ2 But yes, lots of RAM
- HorstG 7y agoI think the optimal number of RAIDz5 disks is 3, if you just want performance. But this wastes lots of space of course. Also, the number of SAS/SATA-channels per controller and the topology of expanders is important. Thats why I don't think there is a recipy, you have to try it out for each new kind of hardware. And as another thread pointed out, stripe size is also an important parameter.
- sokoloff 7y agoI think you mean RAIDZ1, not 5.
- HorstG 7y agoYes. RAIDz (without the "1") was the original RAID5-equivalent, RAIDz2 is equivalent to RAID6. However since nobody really knows what the hell z1 and z2 is and z1 is easy to mix up with RAID1 for nonZFS people, calling it z5 and z6 is far less confusing.
- chungy 7y agoIt's the number of parity disks, pretty simple. There has been occasional talk of making the number arbitrary, though presently only raidz1, raidz2, and raidz3 exist.
- montjoy 7y agoLast time I used ZFS write performance was terrible compared to an ordinary RAID5. IIRC Writes in a raidz are always limited to a single disk’s performance. The only way to get better write speed is to combine multiple raidzs - which means you need a boatload if disks.
- HorstG 7y agoWe had a bunch of Thumpers (SunFire X4200) with 48 disks at work, running ZFS on Solaris. It was dog slow and awful, tuning performance was complicated and took ages. One had to use just the right disks in just the right order in RaidZs with striping over them. Swap in a hotspare: things slow to a crawl (i.e. not even Gbit/s). After EoL a colleague installed Linux with dmraid, LVM and xfs on the same hardware: much faster, more robust. Sorry, don't have numbers around anymore, stuff has been trashed since. Oh, and btw., snapshots and larger numbers of filesystems (which Sun recommended instead of the missing Quota support) also slow things down to a crawl. ZFS is nice on paper and maybe nice to play with. Definitely simpler to use than anything else. But performance-wise it sucked big time, at least on Solaris.
- Annatar 7y ago"After EoL a colleague installed Linux with dmraid, LVM and xfs on the same hardware: much faster, more robust." Please let me know which company this is, so I can ensure that I never end up working there by accident. Much obliged in advance, thank you kindly.
- HorstG 7y agoWhy? What is bad about playing around with leftover hardware?
- Annatar 7y agoNothing at all; it's what was done to that hardware that's the travesty here. It takes an extraordinary level of incompetence and ignorance to even get the idea to slap Linux with dmraid and LVM on that hardware and then claim that it was faster and more robust without understanding how unreliable and fragile that constelation is and that it was faster because all the reliability was gone.