Date: Wed, 24 Mar 2010 10:54:14 +1100 From: Andrew Snow <als@modulus.org> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: on st_blksize value Message-ID: <4BA954A6.9030505@modulus.org> In-Reply-To: <4BA8CD21.3000803@freebsd.org> References: <4BA8CD21.3000803@freebsd.org>
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Andriy Gapon wrote: > One practical benefit can be with ZFS: if a filesystem has recordsize > PAGE_SIZE > (e.g. default 128K) and it has checksums or compression enabled, then > (over-)writing in blocks smaller than recordsize would require reading of a whole > record first. Not strictly true: in ZFS the recordsize setting is for the maximum size of a record, it can still write smaller than this. If you overwrite 1K in the middle of a 128K record then it should just be writing a 1K block. Each block has its own checksum attached to it so there's no need to recalculate checksums for data that isn't changing. - Andrew
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