Slicing SSD

[Jay69]

I've a pair of SSD and I want to Slice them so that I could use part of it for L2ARC and Part of it for ZIL. IS that a good idea and if so, how do I do that ?

 

[gea]

I've a pair of SSD and I want to Slice them so that I could use part of it for L2ARC and Part of it for ZIL. IS that a good idea and if so, how do I do that ?

Mostly a bad idea.
A L2ARC needs not to be mirrored, but you may use both for L2ARC
A ZIL is only used on sync writes. To help, it must be really fast for small writes or its worthless. If your data are critical, use a mirror.

You should not try to slice and mix!

read some basics at:
http://www.nex7.com/readme1st
or (not up to date always)
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide

 

[2g33k4u]

Sort of on the same subject. SSD wasted space.

I recently install Openindiana with nappit.
I included a 128gb SSD for caching and the system is only using 2gb of this drive it seems like a huge waste of space.

What are my options to get more bang for the buck out of this SSD?

Can i put the OS on the drive and have like a 8gb partition and put the l2arch there?

I am not mirroring would that be an exception for l2arch / zil combo?

I just don't want to waste 126gb of SSD.

I am new to openindiana and nappit so please try and make it simple

Am i better off using a class 10 thimb drive in place of the ssd?

 

[Jay69]

I guess if it increase my IOPS by 10 times, then the 2GB isn't wasting space.. but yeah, that's the same reason why I'm asking about slicing SSD so that I can use part of it for the ZIL and part of it for the L2ARC.

I recently install Openindiana with nappit.
I included a 128gb SSD for caching and the system is only using 2gb of this drive it seems like a huge waste of space.

What are my options to get more bang for the buck out of this SSD?

Can i put the OS on the drive and have like a 8gb partition and put the l2arch there?

I am not mirroring would that be an exception for l2arch / zil combo?

I just don't want to waste 126gb of SSD.

I am new to openindiana and nappit so please try and make it simple

Am i better off using a class 10 thimb drive in place of the ssd?

 

[Jay69]

Well, the question is that what is FC and FCoE ? Is it sync write or async writes ? I couldn't find more.
I also read that you do not need mirror for ZIL and L2ARC, so question is how much of performance improvement do I get with a SSD ZIL ? I'm convinced of the benefits of L2ARC but still confuse on how much benefits do I get with ZIL device since it's just 2 x 5 or 10 secs worth of data.

The other question seems to be the memory requirements of deduplication, how much memory would I need assuming I have a ZPOOL of 6T ? I seems to get conflicting numbers based on block size, where do I set these block size ?

Mostly a bad idea.
A L2ARC needs not to be mirrored, but you may use both for L2ARC
A ZIL is only used on sync writes. To help, it must be really fast for small writes or its worthless. If your data are critical, use a mirror.

You should not try to slice and mix!

read some basics at:
http://www.nex7.com/readme1st
or (not up to date always)
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide

 

[gea]

Well, the question is that what is FC and FCoE ? Is it sync write or async writes ? I couldn't find more.
I also read that you do not need mirror for ZIL and L2ARC, so question is how much of performance improvement do I get with a SSD ZIL ? I'm convinced of the benefits of L2ARC but still confuse on how much benefits do I get with ZIL device since it's just 2 x 5 or 10 secs worth of data.

The other question seems to be the memory requirements of deduplication, how much memory would I need assuming I have a ZPOOL of 6T ? I seems to get conflicting numbers based on block size, where do I set these block size ?

FC and iSCSI is only protocol. Sync writes depends on your app and your Logical Units as
far as i see. So its a setable option security vs performance.

You must mirror a ZIL otherwise logged data may be lost in case of a failure
(not data on pool, only last transaction)

Regarding speed: write performance and I/O of sync writes are equal the performance
of your ZIL. Other writes goes directly to RAM which may be up to 10x faster.
All depends on your configuration and more on your workload. If you can accept a sudden
power failure and a dataloss of the last few seconds, you can disable sync write for maximal performance.

If you need nearly the same with sync writes you need a pair of expensive DRAM ZIL.
SSD's (the fast ones with Supercapacitor) are for the rest of us

read: www.ddrdrive.com/zil_accelerator.pdf

 

[Jay69]

ZIL logged data is losted only if the ZIL fail when the system crashed right, otherwise, my understanding is that the actual write is from RAM to HDD and not from ZIL to HDD. That's my read of it. Can I increase the ZIL so that it uses and have a longer gap before it has to write to the HDD from RAM ?

How do I find out if my SSD has capacitor, don't seems to see that written anywhere. In my testing works out, I may want to spec out a better SAN with better performance, more spindle,etc.. so would really appreciate any help.

FC and iSCSI is only protocol. Sync writes depends on your app and your Logical Units as
far as i see. So its a setable option security vs performance.

You must mirror a ZIL otherwise logged data may be lost in case of a failure
(not data on pool, only last transaction)

Regarding speed: write performance and I/O of sync writes are equal the performance
of your ZIL. Other writes goes directly to RAM which may be up to 10x faster.
All depends on your configuration and more on your workload. If you can accept a sudden
power failure and a dataloss of the last few seconds, you can disable sync write for maximal performance.

If you need nearly the same with sync writes you need a pair of expensive DRAM ZIL.
SSD's (the fast ones with Supercapacitor) are for the rest of us

read: www.ddrdrive.com/zil_accelerator.pdf