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I would have to see proof that is was low ram that caused the data loss. The Recommendations for higher amounts memory comes from the way ZFS Caching works. T

I would have to see proof that is was low ram that caused the data loss. The Recommendations for higher amounts memory comes from the way ZFS Caching works. There are 2 caches, ARC and L2-ARC. L2-ARC has to be defined on a SSD and is optional. ARC will always exist and ZFS will use every bit of free memory you have (unless you change the configuration to limit it) to build the cache.. why ram is faster that is why. So the only scenario I could conceive of that would result in data loss is if you are writing files to the ARC faster than ZFS can commit them to disk but that seems unlikely and ZFS should not allow this anyway. for Enterprise work loads the Recommend amount of Memory is 1GB per TB of storage. This is for best performance, however my home server is 35TB and ran for about 2 years with 8GB, and recently upgraded the system to a new proc, mainboard and 16gb a memory, have had no issues with either. I have about 2-3 Movies streaming from it with about 3-4 devices/computers connected for network file storage. The more RAM you give ZFS the better performance you get (to a point) but I believe this issue is massively over talked about and hyped.

leonroy 11y ago
> The more RAM you give ZFS the better performance you get (to a point) but I believe this issue is massively over talked about and hyped. Definitely not hyped as you said in the enterprise space - think some home users see that warning of 1GB per 1TB though and get put off. In my experience we were running multiple vSphere NFS volumes on several large 16x bay FreeNAS systems. We started with 16x 1TB disks and 16GB of RAM. It wasn't until we installed 32GB of RAM before performance became acceptable. Ideally we should really have put in 64GB of RAM but alas Intel's damn Ivy Bridge E3 range maxed out at 32GB. I should stress we were only running 20 virtual machines in total so nothing massively onerous, but that extra RAM made all the difference.
- the_ancient 11y ago
  >We started with 16x 1TB disks and 16GB of RAM. Type of Drives, did you have a L2 ARC and ZIL... There are alot of reasons why you may have needed the additional ram. If you were using off the Shelf 7200 (or worse 5400) NAS drives then I am not shocked, these drives are for storage not for VM's. need atleast 10K drives for VM storage >Definitely not hyped as you said in the enterprise space - think some home users see that warning of 1GB per 1TB though and get put off. It still kinda is, but 90% of the questions I see posted in various places are about Home and Test Labs, not Enterprise Deployments. you do not need 32GB of RAM for your home file server that is likely serving less than 10 clients.
takeda 11y ago
Few minor things. ARC actually is optional, and in fact FreeBSD disables it by default if you have less than 2GB RAM. 1GB per TB or more like 5GB per TB is rule of thumb if you use deduplication. If you don't use deduplication it's more of: "the more RAM you have the better performance you get for reading" ARC is not for writing. It's purely used for improving read performance. For improving write performance you use ZIL device. ZIL is essentially a journal. If you don't specify ZIL device ZFS will store it on data disks. If writing performance is important it is recommended to keep ZIL on separate device (especially SLC SSD). More about ZIL: http://nex7.blogspot.com/2013/04/zfs-intent-log.html http://nex7.blogspot.com/2013/04/zfs-intent-log.html

leonroy 11y ago

> The more RAM you give ZFS the better performance you get (to a point) but I believe this issue is massively over talked about and hyped. Definitely not hyped as you said in the enterprise space - think some home users see that warning of 1GB per 1TB though and get put off. In my experience we were running multiple vSphere NFS volumes on several large 16x bay FreeNAS systems. We started with 16x 1TB disks and 16GB of RAM. It wasn't until we installed 32GB of RAM before performance became acceptable. Ideally we should really have put in 64GB of RAM but alas Intel's damn Ivy Bridge E3 range maxed out at 32GB. I should stress we were only running 20 virtual machines in total so nothing massively onerous, but that extra RAM made all the difference.

the_ancient 11y ago
>We started with 16x 1TB disks and 16GB of RAM. Type of Drives, did you have a L2 ARC and ZIL... There are alot of reasons why you may have needed the additional ram. If you were using off the Shelf 7200 (or worse 5400) NAS drives then I am not shocked, these drives are for storage not for VM's. need atleast 10K drives for VM storage >Definitely not hyped as you said in the enterprise space - think some home users see that warning of 1GB per 1TB though and get put off. It still kinda is, but 90% of the questions I see posted in various places are about Home and Test Labs, not Enterprise Deployments. you do not need 32GB of RAM for your home file server that is likely serving less than 10 clients.

takeda 11y ago

Few minor things. ARC actually is optional, and in fact FreeBSD disables it by default if you have less than 2GB RAM. 1GB per TB or more like 5GB per TB is rule of thumb if you use deduplication. If you don't use deduplication it's more of: "the more RAM you have the better performance you get for reading" ARC is not for writing. It's purely used for improving read performance. For improving write performance you use ZIL device. ZIL is essentially a journal. If you don't specify ZIL device ZFS will store it on data disks. If writing performance is important it is recommended to keep ZIL on separate device (especially SLC SSD). More about ZIL: http://nex7.blogspot.com/2013/04/zfs-intent-log.html http://nex7.blogspot.com/2013/04/zfs-intent-log.html