[lustre-discuss] JBOD or Linux Software RAID0 for OSTs with HA

Pinkesh Valdria pinkesh.valdria at oracle.com
Wed Jan 8 11:04:10 PST 2020

I wanted to ask, what is the best practice when it comes to building the OST.   We have Block volumes we can provision and each of them can deliver 480 MB/s throughput and they can be attached to multiple compute nodes in sharable read/write mode.   I have a 25Gbps (3125 MB/s)  network between OSS and Storage devices (aka: block volumes).   Lustre clients nodes also have 25Gbps network connection to OSS nodes. 


On OSS servers,  I setup 7 or more OST’s (7*480=3360MB/s) and set Stripe Count to 7 or more,  to ensure clients get max throughput performance possible. 
On OSS servers,  I setup a Linux software RAID0 of 7 block volumes,  set Stripe count = 1 ,  to ensure clients get max throughput performance possible.   I can setup multiple OSTs for the OSS, with each OST been a RAID0 of 7 block volumes.   

Question:  Is it better to use Option2 or let clients use stripe count 7 or more, to get the max performance from the file system.   Most clients will use 1 File per process when writing files to file system.   With Option2,  I am trying to hide the Storage backend throughput complexity from clients.  


Our Block volumes are already replicated, so I don’t need to do RAID1, RAID5 or RAID6 at the Linux s/w RAID level.  In option2,  I am using RAID0, so I can get throughput from 7 Block volumes which matches the network speed I will have between most of my Lustre clients and Lustre OSS servers.  


Another question is,  has anyone implemented HA across 2 OSS nodes pair/building block and using OST’s which are linux software RAID0.    Issue I am facing is after I create RAID0 on OSS1,  I have to reboot OSS2 to make it visible on OSS2.   Then if I reboot OSS1,  the RAID0 (/dev/md127) is gone on OSS1.  Wondering if this is technically even feasible to have HA with Linux software RAID0 ?






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