Take the 2-minute tour ×
Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

I am thinking about building a database system with iSCSI. But now I am thinking about the WAL. WAL shouldn't lag.

WAL is implemented with a ring buffer, isn't it? So if I only care about the thoughput of big write transactions, then iSCSI performance shouldn't be affected?

Has someone got experience on this subject, will I bottleneck myself?

share|improve this question

migrated from stackoverflow.com Oct 3 '11 at 12:35

This question came from our site for professional and enthusiast programmers.

Which database? –  Basil Oct 3 '11 at 14:40

1 Answer 1

Most databases are mostly concerned with random reads, normally 70% of their activity. This leads to lots of disk seeks, and the key performance metric is IO/s. You say you only care about the throughput of big writes, though. For this, iSCSI is less ideal than some non-IP option, however can be made to work.

iSCSI is limited by being non-duplex, as reads and writes share bandwidth. If you want to maximize throughput, you will want to have as large a dedicated IP pipe as you can get to your iSCSI disks. Potentially you could use more than one cat 6 cable, or even a 10Gb/s link. Your maximum throughput would be between 80-95% of line speed, based on the amount of packet collision overhead you get.

A fibre channel connection would go 8Gb/s per path duplex. That means no matter how much returning traffic (scsi acknowledgements, etc) you have, you will always have 8Gb/s of write bandwidth.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.