Date: Thu, 11 Sep 2014 11:46:50 +0100 From: Pete French <petefrench@ingresso.co.uk> To: ari@ish.com.au, freebsd-stable@freebsd.org, petefrench@ingresso.co.uk, se@freebsd.org Subject: Re: getting to 4K disk blocks in ZFS Message-ID: <E1XS1tq-000IW6-DB@dilbert.ingresso.co.uk> In-Reply-To: <54117624.7020907@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
> There is no problem, if ashift covers more than 1 sector, except > that you waste some space. If ashift=12 is used with 512 byte > sectors, then all writes will be to 8 consecutive sectors. There > is no read-modify-write as in the opposite case (ashift=9 with 4K > sectors). But what if one of those 8 writes fails ? ZFS understands that part of a write can fail then ? or does it think of it as 8 separate writes ? > But the amount of wasted space can be quite substantial. I have > read reports of some 8% less usable space with ashift=12 compared > to ashift=9, for an empty ZFS file system. And with lots of small > files, this will become worse, once the file system is filled. Yes, I have migrated a lot of filesystems over to 4k, and there is quite a lot of extra space taken up by the same amount of data - even wth lz4 compression enabled, which I do on most systems. However the extra performance is well worth it. Only reason I am asking is that I am thinking of migrating a zpool which only has one 4k drive in it, plsy 3 512byte ones. Just want to make sure that it is not a bad idea to do this. -pete.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?E1XS1tq-000IW6-DB>