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On 09/04/18 19:00, Vincent Royer wrote:<br>
<blockquote type="cite"
cite="mid:CAL4nCoPJ22Zg3thV1iKnijf0S93uzf90iP2k8-UgNoZh32M54A@mail.gmail.com">
<div dir="ltr">Yes the flash-backed RAID cards use a
super-capacitor to backup the flash cache. You have a choice of
flash module sizes to include on the card. The card supports
RAID modes as well as JBOD.
<div><br>
</div>
<div>I do not know if Gluster can make use of battery-backed
flash-based Cache when the disks are presented by the RAID
card in JBOD. The Hardware vendor asked "Do you know if
Gluster makes use of flash-cache in JBOD?"</div>
<div><br>
</div>
<div>If it does, I'm not certain how the size of this flash
cache affects the operation. </div>
</div>
<div class="gmail_extra"><br>
</div>
</blockquote>
<font size="4"><font face="arial narrow, sans-serif"><b><br>
</b></font></font><font size="4">I thought you wanted to use ZFS
underneath Gluster? You need to state your use case properly so we
can help you.<br>
<br>
Pretty much any RAID card I've come across does not use the
on-board cache (which is always RAM, backup up with a BBU or a
Flash chip(s)+Supercaps) when set to JBOD mode. You could use a
RAID controller with GlusterFS with XFS or EXT4 underneath but it
why not just use the redundancy built into GlusterFS? You could
still use software RAID if you're really concerned about your
data.<br>
<br>
If you're using ZFS you don't even want to use a RAID
firmware/card set to JBOD mode, you need an HBA or a dual-purpose
RAID/HBA card running the HBA firmware (IT-mode in
LSI/Avago/Broadcom cards, eg IBM M1015, 1115). <br>
<br>
Even if you use XFS or EXT4 underneath Gluster I'd still look at
leaving out a RAID capable controller, as if you can't get the
same model and the card fails you can't just plonk the drives into
any other box with SATA/SAS ports and just carry on as before. <br>
<br>
In either case, don't use desktop drives as they often lie about
if they flush their own RAM cache. Use nearline enterprise SATA or
SAS drives.<br>
<br>
Part of the point of GlusterFS and ZFS is it's "software defined",
you use fast but dumb drive controllers so you don't have to ever
worry again about hardware compatibility and availability, it's
all in the OS/FS stack and the hardware conforms to open
standards.<br>
<br>
Eg:<br>
<br>
Client apps > GlusterFS > ZFS | > HBA > JBOD<br>
Client apps > GlusterFS> XFS | > HBA > JBOD<br>
<br>
All the caching, resilience, failover is handled above the place
where I've put the pipe character. This means your HBA and
enclosures can go up in smoke, as long as you still have the
drives you'll have your data.<br>
<br>
What are your plans WRT your underlying brick FS? ZFS or other?<br>
<br>
<br>
<br>
<br>
<br>
<b></b></font><font size="4"><font face="arial narrow, sans-serif"><b></b></font></font>
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