DC P3700 SSD & block size: 8192B configured, 131072B native "warning"

[johwes]

Hi All,

I haev two Intel DC P3700 SSD 400GB PCI-SSD thai i try to use as ZIL & L2ARC but i get this block size "warning" when i add them to my pool.

Shuld i do anything different or is it ok to leave it like that?

logs
mirror-18 ONLINE 0 0 0
gpt/log1 ONLINE 0 0 0 block size: 8192B configured, 131072B native
gpt/log2 ONLINE 0 0 0 block size: 8192B configured, 131072B native
cache
gpt/cache1 ONLINE 0 0 0 block size: 8192B configured, 131072B native
gpt/cache2 ONLINE 0 0 0 block size: 8192B configured, 131072B native

 

[Spearfoot]

Hi All,

I haev two Intel DC P3700 SSD 400GB PCI-SSD thai i try to use as ZIL & L2ARC but i get this block size "warning" when i add them to my pool.

Shuld i do anything different or is it ok to leave it like that?

logs
mirror-18 ONLINE 0 0 0
gpt/log1 ONLINE 0 0 0 block size: 8192B configured, 131072B native
gpt/log2 ONLINE 0 0 0 block size: 8192B configured, 131072B native
cache
gpt/cache1 ONLINE 0 0 0 block size: 8192B configured, 131072B native
gpt/cache2 ONLINE 0 0 0 block size: 8192B configured, 131072B native

You have two P3700 drives, but your listing shows twice that many devices (2 log and 2 cache).

Did you partition these drives, using one partition for log and the other for cache? Because that's not a good idea at all.

 

[johwes]

You have two P3700 drives, but your listing shows twice that many devices (2 log and 2 cache).

Did you partition these drives, using one partition for log and the other for cache? Because that's not a good idea at all.

Hi,

Can you pleace explain way it not a good idea? I Think it can handle my network connection and i get faster with that setup then without. Or do i miss somthing?

 

[Spearfoot]

Hi,

Can you pleace explain way it not a good idea? I Think it can handle my network connection and i get faster with that setup then without. Or do i miss somthing?

There are quite a few threads about this very subject here on the forum. In a nutshell, L2ARC cache and ZIL SLOG devices have wildly different device requirements: L2ARC should be big - roughly 4 or 5 times the size of RAM installed on the system - and read-optimized; a ZIL SLOG device doesn't need to be large at all, but needs power protection, low latency, fast writes, high durability, and should be write-optimized.

Your Intel P3700 devices are well-suited for use as ZIL SLOG devices, BTW. They're overkill for L2ARC, where larger and cheaper devices are adequate to the purpose.

If you use the same device for both purposes, you'll suffer I/O contention because of the differing requirements, among other things, as discussed in these threads:

https://forums.freenas.org/index.php?threads/partition-ssd-for-zil-l2arc-and-pool.29004/
https://forums.freenas.org/index.php?threads/zil-and-l2arc-on-same-disk.23333/
https://forums.freenas.org/index.php?threads/finding-suitable-zil-and-l2arc-drives.13561/

Regarding L2ARC: In general, you shouldn't add an L2ARC device until/unless you've installed the maximum RAM on your motherboard and are still experiencing poor performance. Because of memory overhead, adding an L2ARC to systems with less than 64GB of RAM can actually have a negative impact on performance.

Regarding ZIL SLOG: You don't need a SLOG device unless you are providing storage for virtual machines via either NFS or especially block storage via iSCSI. For this particular use-case, you need to enable synchronous writes on the VM dataset; without a ZIL SLOG device, synchronous writes drastically affects write speed. Also, if you want good performance for a VM datastore the standard procedure is to use multiple mirrored vdevs instead of large RAIDZ arrays because IOPS scale with the number of vdevs.

You haven't posted your system specs or told us how you intend to use your FreeNAS system, so we can't make specific recommendations for you... But at the very least, dedicate one of the P3700s as a SLOG device and the other as L2ARC, instead of mixing partitions.

 

[mav@]

What's about the block size warning -- I believe it should be fixed in latest FreeNAS versions. ZFS has can not really optimize for physical block sizes above 8K, what it tried to do before, and so from one side those complains have no sense, while from another optimizing to 8K instead of 128K, as reported, is in fact a pessimization and should no longer be done for pools created (or vdevs added) by modern FreeNAS versions.

 

[johwes]

What's about the block size warning -- I believe it should be fixed in latest FreeNAS versions. ZFS has can not really optimize for physical block sizes above 8K, what it tried to do before, and so from one side those complains have no sense, while from another optimizing to 8K instead of 128K, as reported, is in fact a pessimization and should no longer be done for pools created (or vdevs added) by modern FreeNAS versions.

I just tried this in the latest FreeNAS 10.0.3 and still gets this "warning" when i tried to add it to the new created pool.
But can I just use it like it is or will effect the performance?

But this two SSD is for my zil mirror i have two 10gbit net connections so I think I just need maximum 20g of ZIL.
What will be the correct way to part & format and add those so I don't lose speed. its two Intel DC P3700 SSD?

 

[Spearfoot]

Ijust tried this in the latest freenas 10.0.3 and still gets this "warning" when i tryed to add it to the new created pool.
But can i just use it like it is or will effect the performance?

but this two ssd is for my zil mirror i have two 10gbit net conections so i think i just need maximum 20g of zil.
what will be the correct way to part & format and add those so i dont lose speed. its two Intel DC P3700 SSD?

According to iXsystem's "To SLOG or not to SLOG: How best to configure your ZFS Intent Log" article, you need 6.25GB for each 10Gb connection, so 12.5GB would be plenty of space. I would use 16GB, 'cause I'm a programmer and I like powers-of-2. :)

You don't really have to partition the drives, but I do on my systems based on the idea that doing so will increase the longevity of the SSDs. I always refer to the "SSD Over-provisioning using hdparm" article at Thomas-Krenn when I configure a new SLOG drive, which describes increasing the spare area using Linux. But I suppose you could just partition the drive, too.

Good luck!

 

[mav@]

It seems this bug is immortal. Fixed it again: https://bugs.freenas.org/issues/23233