t1066

回復 40# ipsec

While I generally agree with what you said, there are a few points that I want to make:

1. The purpose of using cache drive is foremost to increase the IOPs of the system. That is why we are seeing technologies like Intel smart response, hybrid drive Seagate momentus XT or LSI cachecade.

2. Dedup. When using Dedup, the requirement for RAM jumps significantly. It would be prudent to have spare capacity in the form of SSD to fall back to. Otherwise, the performance of the pool will plummet.

3. It is possible to use ZFS with some old computer parts. Such systems would only have 1-2G of RAM. They could benefit from an SSD or a fast USB flash drive as cache drive.

4. It is not recommended to use ZFS over hardware RAID. Not only do you  lose one important feature of ZFS: detect and correct data error, your pool would not be portable.

ipsec

回復  ipsec

While I generally agree with what you said, there are a few points that I want to make ...
t1066 發表於 2011-9-10 12:08

Thanks for your response.

From your pt. 1&2, in my point of view, the technology of Intel smart response, hybrid drive..., came out are targeted to low end PC/Server market. That's why we can buy it from PC market. If there are enough of system memory for the taking advantage of ZFS with a small disk storage required, why does HOME/SOHO users going with SSD as cache for the price added?

3.  For the old computer parts, it is less of CPU power to take the ZFS others
feature, such as data integrity (SHA-2) throughout the file system tree and
data encryption. The ext3 filesystem is more suitable for old computer parts.

4.  For the hardware RAID on ZFS, how about to build two physical disks(set) in hardware RAID-0/1 and configure five RAID-0/1 (as a example) sets in ZFS pool. I haven't tested this approach, have you?

Happy discuss,
cheer

t1066

回復 42# ipsec

Thanks for your feedback.

1&2. I have to agree with you that in many cases, adding an SSD would not be necessary. However, in some cases, having 32G RAM + 120G SSD (think of is as cheaper but slower RAM instead of more expensive but smaller HDD) would be beneficial, e.g. lower latency of the system.

3. Unless you are using Dedup, you should use fletcher4 instead of sha256 for checksum. Also, ZFS offer self healing of data. So it would be down to your needs.

4. I would just list a few objections for using hardware RAID with ZFS: increasing system complexity, you have to add spare drives to each of the RAID subsystem instead of adding them to the whole pool, hardware dependency.

Cheers.

ipsec

回復  ipsec

4. I would just list a few objections for using hardware RAID with ZFS: increasing system ...
t1066 發表於 2011-9-11 11:44

Agree. It is a general question of the hardware RAID pros and cons.