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List:       zfs-discuss
Subject:    Re: [zfs-discuss] best way to configure raidz groups
From:       Erik Trimble <Erik.Trimble () Sun ! COM>
Date:       2009-12-31 17:30:01
Message-ID: 4B3CDF99.7040903 () sun ! com
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Thomas Burgess wrote:
>
>
>     For the OS, I'd drop the adapter/compact-flash combo and use the
>     "stripped down" Kingston version of the Intel x25m MLC SSD.  If you're
>     not familiar with it, the basic scoup is that this drive contains half
>     the flash memory (40Gb) *and* half the controller channels (5 versus
>     10) of the Intel drive - and so, performance is basically a little
>     less than half although read performance is still very good.  For more
>     info, google for  hardware reviews.  This product is still a little
>     hard to find, froogle for the following part numbers:
>
>     Desktop Bundle - SNV125-S2BD/40GB
>     Bare drive - SNV125-S2/40GB
>
>     Currently you can find the bare drive for under $100.  This is bound
>     to give you better performance and guaranteed compatibility compared
>     to adapters and compact flash.
>
>     The problem with adapters is that, although the price is great,
>     compatibility and build quality are all over the map and YMMV
>     considerably.  You would not be happy if you saved $20 on the
>     adapter/flash combo and ended up with nightmare reliability.
>
>     The great thing about 2.5" SSDs is that mounting is simply a question
>     of duct tape or velcro! [ well .... almost ... but you can velcro them
>     onto the sidewall of you case ]  So you can use all your available
>     3.5" disk drive bays for ZFS disks.
>
> I was able to find some of the 64 gb snv125-S2 drives for a decent 
> price.  Do these also work well for L2ARC?
>
> This brings more questions actually.
>
> I know it's not recommended to use partitons for ZFS but does this 
> still apply for SSD's and the root pool?
>
> I was thinking about making maybe using half of the ssd for the root 
> pool and putting the ZIL on the other half.
>
> Or would i just be better off leaving the ZIL on the raidz drives?
>

It's OK to use partitions on SSDs, so long as you realize that using an 
SSD for multiple purposes splits the bandwidth into the SSD across 
multiple uses.   In your case, using an SSD as both an L2ARC and a root 
pool device is reasonable, as the rpool traffic should not be heavy.

I would NOT recommend using a X25-M or especially the snv125-S2 as a ZIL 
device.   Write performance isn't going to be very good at all - in 
fact, I think it should be not much different than using the bare 
drives.   As an L2ARC cache device, however, it's a good choice.

Oh, and there's plenty of bay adapters out there for cheap - use one.  
My favorite is a two-SSD-in-1-floppy drive bay like this:

http://www.startech.com/item/HSB220SAT25B-35-Tray-Less-Dual-25-SATA-HD-Hot-Swap-Bay.aspx

(I see them for under $40 at local stores)


20GB for a rpool is sufficient, so the rest can go to L2ARC.  I would 
disable any swap volume on the SSDs, however. If you need swap, put it 
somewhere else.

-- 
Erik Trimble
Java System Support
Mailstop:  usca22-123
Phone:  x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)

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