I've got two new SSD's that I want to set up as RAID1 and use strictly
for the OS and MySQL DB's partitioned accordingly.
I'll be using the 3.4.6 kernel for now in openSuSE 12.2 with ext4. So
after a lot of Google'n and reading it is my understanding that discard
is not sent to the devices via the raid drivers. I am aware of Shaohua
Li's patches to make it work but am not inclined to use them due to
openSuSE's Online Update replacing the kernel. I'm not against patching
and gen'ing a kernel, that used to be SOP, but just don't want deal with
that overhead. Of course unless I really need to.
So I've read, and if I understand things correctly, I can use LVM and
RAID1 and the the discard commands will be sent to the devices. Is that
correct and currently the only way or is/are there other ways?
I've also read that a lot of people are saying TRIM isn't needed because
the SSD's garbage collection is so good now TRIM isn't needed. But I
don't see how that could work because the SSD's don't have access to the
file system so they don't know which pages in the blocks are marked
unused to do any consolidation and erasing. And using TRIM is suggested
in a OCZ document I read and who's drives these are. Unless, the SDD
when it has to change a page moves the whole block then erases the old
block? But without TRIM in could be moving invalid data too because it
doesn't know that and that to me sure doesn't sound efficient and this
operation would be a perfect time to get rid of the invalid data if it
did know.
And due to PEC I'm wondering if this is even a good idea? Granted the OS
files can be considered somewhat static, with the exception of /var/log
so maybe that shouldn't go on the SSD, and maybe MySQL shouldn't either
because for things like ZoneMinder it's DB is pretty dynamic. But with
all the logging going on, and there is a lot, and the dynamic nature of
the MySQL data is the exact reason I want it put it on SSD's, for the
speed. See my quandary?
This is my best understanding of things right now so I came here to and
am asking the experts for help in clarifying and understanding this and
pick the best direction to go. Have the SSD's for a couple of weeks now
but holding off using them until the I can determine the best way to use
them. Oh and the SSD's are OCZ Vertex 4 VTX4-25SAT3-256G.
Thanks.
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