`<div dir="ltr"><div>The 840 Pro doesn't have a super cap, but it does properly honor cache flushes which ZFS will do on a log device. This drastically reduces it's write performance and makes it a poor choice for a log device.<br>
<br></div><div>Intel has several SATA SSDs with proper super-cap protected caches that make good log devices. They are nothing like a ZeusRAM, but will protect your transactions.<br></div><div><br></div><div>Keep in mind vSphere is a 100% sync write NFS client. If the log device doesn't perform well, neither will vSphere. <br>
<br></div><div>If you trust your backups I would stick to ZIL disabled. If you want to do HA, you need to look at an all SAS solution, which is not cheap. <br><br>-Chip<br></div><div><br></div></div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Wed, May 28, 2014 at 8:51 AM, Dan Swartzendruber <span dir="ltr"><<a href="mailto:dswartz@druber.com" target="_blank">dswartz@druber.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
(merging comments to Saso and Jim)<br>
<br>
I don't think I mentioned my environment - if not, my apologies. This is<br>
a SOHO/Lab setup, so things like zeusram are non-starters. The basic<br>
network infrastructure is gigabit, so iSCSI ZIL would suck badly, I<br>
suspect. As far as over-provisioning the 840PRO, I have it sliced for<br>
16GB. Once it's been running for awhile, I will re-run the disk<br>
benchmark. I understand the 840PRO doesn't have a supercap - this was<br>
basically just a performance analysis to see how it stacks up compared to<br>
sync=disabled and on-pool ZIL. If I go this route, I will need to look<br>
for a decent/affordable unit with supercap. One other test I can try is<br>
with a 15K 76GB SAS 2.5-inch drive I salvaged from a dead server. It<br>
should have about 1/2 the latency of a 7200rpm sata drive, and if so would<br>
get me up to about 40MB/sec, which is still not good, but better than<br>
on-pool ZIL. I'll find out later. I have googled a fair amount and there<br>
seems to be 'work in progress' for TRIM support for ZoL and illumos, but<br>
no real indication I could find as to when either might support it.<br>
<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
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