Need help on Read throughput

[Kiranv]

I am new to ZFS and would be glad if anyone can help me with the following query.

We are using the ZFS pool for our Backup and restore services and we access the files on need basis. The problem is the first time reads are very slow (getting 1.15 GBps read throughput) and we are getting very good read throughput while accessing the same files second time( disk reads are very minimal in second time and getting 20GBps throughput). Is there any process or command to put the files in memory at NAS server side before the start of application access. we have plenty of RAM available at NAS servers( 4 nas servers * 230 GB) and RAM may not be an issue for us.

Appreciate your help in advance.

 

[Chris Moore]

What you are experiencing is the file being loaded into ARC such that the second time it is accessed it is pulled from RAM instead of from disk. You could make the first access faster by re-configuring the disk pool, but the ARC (Adaptive Replacement Cache) is part of how ZFS works. There are some adjustments that can be made. You might get some tips from watching this video:
https://www.youtube.com/watch?v=oDbGj4YJXDw&t

 

[Kiranv]

Thanks Chris Moore for the info. We have tweaked the record size and other tunables and we are getting same throughput for read and wright.